"I hate 'em, I hate 'em, I hate 'em!" Mary Lou screamed as she mashed the class's two cultures of green algae with her razor blade. "I have had enough of you, you Acetabularia, you simple, single-celled, slimy bits of fuzz!" She marched out of that 1936 lab and slammed the door behind her rattling the glass in its frame. "I don't want to study little cold things like you anymore. I want something big and warm and fuzzy."

    She stomped right past her brother Jason, who was sitting on the college's north front stoop with his friend Wilbie, and did care one little bit - for sure and for certain - about talking about the two different species of Acetabularia - both stalked but one roundish and the other frilly. To make matters worse for her mood, she saw Jimmy - with Cheryl walking too close - entering the south entrance to the building.

    The next day when Mary Lou dispondently entered the lab late she found her classmates each huddled over their dissecting scopes pushing the little algae around. But it was the fact that Prof. Bengston had his own eyes glued to a scope that told her that something was happening - as he was usually blasé about what was being viewed. "Yup, here's another one, and another," he mumbled. "Cheryl, that was a great observation you made yesterday afternoon." (Now, if that didn't beat all, Mary Lou thought to herself. More praise for Cheryl!)

    Prof. Bengston related to the rest of the class that when Cheryl and Jimmy had returned to set up for the next day, they found that some vandal had come in and sliced up all the Acetabularia. To determine the extent of the devastation, Cheryl scoped the two cultures and found that in both, some parts were withering and yet other parts were regenerating what was cut off. More specifically that detached tops withered but the bottoms were beginning to grow back their missing tops. And - much to Mary Lou's chagrin - Jimmy seemed really interested and joined with Jason and Wilbie to suggest next-steps to be taken.

    Not to be ignored, Mary Lou blurted out: "If y'all love those things so much why don't you glue 'em back together." All eyes turned disparaging on her but then Jason's expression changed. "Yeahhh-, let's see if we can graft them."

    While the others did not find this to be at all difficult, Mary Lou knew she had to do something different - how else could she attract Jimmy's attention - ah, affection? So she started cutting off the tops from frilly ones and trying to graft those onto freshly trimmed round bottoms, and vice versa (as in the next figure below). But her heart wasn't in it and she pushed her dishes aside, sighed, got up and walked out muttering that she would never get a good grade in this class for which she had so little interest.

    At 10 that evening, she wandered in from the ice cream parlor and her mother told her that Jason had run home to say that Mary Lou was to get to the lab as soon as possible - and that she ought to clean up and fix her face so she'll be ready.

    "Ready for what?" she asked her mother.

    "I have no idea, but your brother was extremely excited."

    So Mary Lou gussied up in her new Wards dress and trudged on over to the school. From outside she saw the lab lights all lit up and lots of silhouettes moving around in the room. When she entered the room, lots of cheers went up for her, and once again she wondered what she had done to receive all these accolades.

    They pushed her over to look in one of the scopes, and when she saw what is shown to the right, she thought to herself "So what?" But she paaaaainted a big smile on her face and said: "By golly, that's amazing!"

    From the various pictures shown here, what really important biological principle was discovered?