In late August of 1967 I was a brand-new high school biology teacher in the suburbs east of Berkeley, California
In late August of 1967 I was a brand-new high school biology teacher in the suburbs east of Berkeley, California. That part of California (most of the state, actually) has a Mediterranean climate in which a cool, wet winter season alternates with a hot, dry summer season. No rain falls between April and September, and between that and the heat, the grass and herbs that make that part of the world so green in the winter and spring are dead before May and the hills stand golden all summer long.
I’ve heard that spring can come from one day to the next in places like Michigan, Minnesota, and Manitoba, but seasons don’t snap into place like that in Central California. They don’t slide smoothly from one to the other, either, because the storms build up and die back in fits and starts. The first thing in the fall might be a spitty little rainstorm that produces hardly enough water to get the windshield wet, then dries back out and gets hot again, sometimes even on the same day. Pretty much like clockwork, the storms get longer and wetter and the fair weather cooler and shorter until everyone knows it is winter. And by Christmas it is as green as Ireland (by late March it is as green as the Hobbits’ Shire).
That first autumn in Walnut Creek, I noticed something wonderful. One morning, a couple of days after a small rainstorm, the previously pure gold slopes of Mt. Diablo were subtly tinged with the lightest shade of green. A day or two later they were gold again, and then the same thing happened after the next rainstorms, until finally the dry spells were cool enough and short enough that the green bridged between the storms and the world looked and felt like winter.
From time to time over the next year, I thought about what I had seen that autumn. Because the bulk of the vegetation on those slopes were annual grasses and herbs, the green couldn’t have resulted from living plants “greening up” - - they had been dead for months. It had to be seeds germinating. But if the slopes turned green from germination and then turned gold again, that must mean that the plants that germinated died before they really got started, and only those that germinated late enough in the autumn would survive to reproduce. But which seeds germinated early and died, and which managed to wait long enough and lived? I wondered.
The first time it rained next fall, I took each of my classes outside to the parking lot to gaze up at Mt. Diablo. Each time, I asked the same question and gave no hints: “Does anyone notice anything different about Mt. Diablo today?” After that first rainstorm, the change was so subtle that none of my 150 students noticed; we went back inside with no discussion, and rumors circulated in the school about my sanity. The next time, a few kids noticed the subtle shift in color, but it wasn’t dramatic enough to capture their imagination. It was a start, though, and we went back outside each day to check the color. Each class noticed that the hills turned gold again, but few of the 10th grade biology students found anything in that to wonder about. I managed to lead them into the discovery that the green must result from germination of seeds, and enticed a few kids to make a bicycle expedition into the hills to check that assumption. They returned with rudimentary notes that confirmed my suspicions, but I didn’t know enough yet about how to stimulate creative thought to get very far with them. I learned mountains about 15-year-olds’ understanding of the natural world and about their reasoning power, and in a sense it set a good part of the curriculum for the rest of the year.
I also taught two sections of a second-year biology course that year, for science “keeners” who had taken biology in 10th grade and had already taken or were concurrently taking upper-level math, chemistry, and physics. It was entirely a research course (see article about another incident from this same class). Most of those students were little more interested in the colour of Mt. Diablo than the younger students were, and although they seemed to appreciate the tooth-and-claw meat of the question about who lived and who died, they got little farther in their reasoning than the other classes did.
One morning, a day or two after a minor storm, Frank Spear came to see me before class. He asked, “Can I take a chair up on the roof today? I want to sit and think about Mt. Diablo.” “Yesss!”, I thought, and after cautioning him not to break his neck or disturb the physics class that would be below him, I gave Frank permission to spend his class time on the roof. He asked the same thing the next day, and every day that week, and the next time he came to class he confronted me.
“I know which seeds germinate after it rains,” he said.
“Well, what do you think?”
Confidently, he replied “It’s the little ones”.
“What do you mean, ‘the little ones’, Frank?”
“Only the smallest seeds can get enough water to germinate after a little storm. The big ones soak up a little bit, but they can’t get enough to germinate and that lets them dry back up again until a storm is big enough and they germinate. It’s the smallest seeds that die and the biggest ones that live.”
“That’s a really interesting idea, Frank, but what makes you so sure it’s right?”
“Well , it makes sense, doesn’t it?”
“It makes a lot of sense, Frank. But just because an explanation makes sense doesn’t make it right. And besides, you haven’t explained yet what makes you think the small seeds can get the water they need but the large seeds can’t.”
Frank didn’t appreciate my conservatism, but he kept working on his argument. Each day he presented a bit more of it, and each day I acknowledged his progress and then pointed out difficulties that still made it difficult for me to completely accept his explanation. Gradually, day by day and with a great deal of frustration at my stubbornness, Frank discovered for himself what he needed to include in his argument. The key was his realization that the relationship between the surface area and the volume of objects varies with their size. That insight allowed him to produce the formal argument that is one of the class handouts in another section of the website.
I freely acknowledged the elegance, the completeness, and the generality of the argument and praised Frank liberally for his accomplishment. But impressive as the deductive argument was, it still didn’t satisfy me. Rather than telling him about the difference between deductive and inductive arguments and trying to influence him to test his hypothesis experimentally, I just worried aloud whether it actually applied to the seeds on Mt. Diablo. Not surprisingly, this frustrated Frank even more. Each day in class, he either sat by himself, apparently brooding, or asked to go to the library. His knowledge of seeds, membranes, germination, weather, and soils expanded enormously, but he remained frustrated that I wouldn’t accept that his formal argument solved the problem we had started with.
One day, Frank came to see me before school started. “What are you doing during your prep period?”, he asked. I said, “I don’t know yet, Frank, but I have a sense that I’ll be doing something with you. What do you need?”
“I want you to take me to the garden store so I can buy some pea seeds. I need round peas, not those wrinkled ones that Mendel studied. If I get wrinkled ones I won’t be able to estimate the surface area and then you’ll complain that my experiment doesn’t answer my question. To find out whether small seeds germinate faster than big ones, they will all have to be the same shape, and if they are round I can calculate their surface area from their diameter.”
“Yessss!”, I thought, and arranged to meet Frank at my car at the beginning of my preparation period.
On the way to the seed store, Frank sketched his experimental design and I suggested a few things to make it easier. We bought every package of round pea seeds they had in the store, and returned to the school. Over the next couple of weeks, Frank gradually refined his experimental approach. He originally planned to measure the diameter of his seeds with a ruler, so I told him about calipers and then arranged for him to weigh them into size classes at a Dow Chemical research station next door to the school.
Frank’s final experimental protocol was beautiful, although it, like the hypothesis that it tested, was born painfully and with much frustration because of my stubbornness. One key issue that was particularly difficult for Frank was just what he would record to indicate when seeds germinated. After much reading, he realized that seeds swell as they absorb water, and at some point the seed coat membrane covering them must rupture. Once that membrane has ruptured, Frank reasoned, the plant must either grow or die. Although he was unable to find data supporting this logic, I agreed to it happily and Frank planned to record the time when each seed germinated.
I placed one more roadblock in his way before he did the experiment. I worried that since Frank didn’t know how long it takes pea seeds to germinate and he had many other things to do in his life beyond watching test tubes, and suggested that there might be a way to estimate, rather than measure, germination time. Because he had some 20 or 30 seeds in each treatment, Frank quickly realized that he could observe test tubes at regular intervals, recording the proportion of seeds in each whose seed coats had ruptured by that time. With an extension of that logic, Frank convinced me that it would not affect the outcome of his experiment if some of the seed coats ruptured on the side away from the glass as long as this error was the same for all the treatments. He planned to observe his test tubes every hour until the last seed had germinated. “The last seed?,” I worried. “What if some of your seeds are dead?” We compromised with some arbitrary proportion.
In each of a set of test tubes arranged randomly in test tube racks, he placed 5 seeds from the same weight category, held against the glass by a tightly rolled piece of paper towel. There were enough seeds to replicate each of his ten weight class treatments several times. He filled each tube with water at Time Zero, then carried his test tubes around with him, checking them every hour of the day and night. And sure enough, the smallest seeds germinated first.