![]() ![]() ![]() Early plants such as ferns have compound leaves in which explicit branching structure is still seen. The fossil record suggests that leaves first arose roughly 400 million years ago, probably when collections of branches which lay in a plane became joined by webbing. Traditional evolutionary explanations have not had much to say about detailed questions of leaf shape one minor claim is that the pointed tips at the ends of many tropical leaves exist to allow moisture to drip off the leaves. My model for leaf shapes is presumably most relevant for initial shapes. It may nevertheless be that leaves on a single plant initially have a discrete set of possible shapes, with variations in final shape arising from differences in environmental conditions during expansion. On a single plant different leaves can have somewhat different shapes-sometimes for example those lower on a tree are smoother, while those higher are pointier. Surgically modifying such buds when they are as small as 0.1 mm can have dramatic effects on final leaf shape, suggesting that at least some aspects of the shape are already determined at that point. At the earliest stages, buds that will turn into leaves start as bumps on a plant stem, with a structure that is essentially impossible to discern. For a long time it was believed that after leaves came out of their buds growth was due mainly to cell expansion, but in the 1980s it became clear that many cell divisions in fact occur, both on the boundary and the interior. Similar but increasingly quantitative studies have been made ever since, and have reported a variety of non-uniformities in growth. Already in 1724 Stephen Hales looked at the motion of grids of marks on fig leaves, and noted that growth seemed to occur more or less uniformly throughout the leaf. But there has been very little general scientific investigation of leaf shapes, and most of what has been done has concentrated on the expansion of leaves once they are out of their buds. (They appear for example in the first edition of the Encyclopedia Britannica from 1768.) Leaf shapes have been widely used since antiquity as a way of identifying plants-initially particularly for medicinal purposes. There are 22 pages of leaf images to be printed in color (two cards per page), and 10 pages of information to be printed in black and white.įor lessons that use this learning material and information for integrating it into biology study, see Life Science Lessons for the Montessori Elementary Classroom by Cynthia Brunold-Conesa.Some classification of leaf shapes was done by Theophrastus as early as 300 BC, and classifications similar to those above were in use by the early Renaissance period. When printed full size, the cards are half-page size, 5.5 X 8.5 inches. Printed cards are available - see " Leaf Shapes & Margins - Printed cards." The species vary from common trees and houseplants to tropical plants that show unique features. Along the way they can marvel at the sheer beauty of leaves.Įach card has a single leaf along with its common and scientific names. They can also measure the angles of the leaf apex and base, and describe the shape of those parts of the leaf. Older children can measure the images and learn to determine the leaf shape mathematically. Younger children can enjoy the images and find features such as lobes, teeth, and venation patterns. ![]() Examples from the five major leaf shapes – elliptic, ovate, obovate, oblong, and linear – are included. This set of 44 beautiful leaf images encourages all ages to observe leaves and see their special features.
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