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The food of the Morning-Glory is called albumen; it does not differ from the others in kind, but only in its manner of storage. Also the questions have brought out the fact that the Bean and Pea have the plumule ready formed in the seed, while the Morning-Glory and Sunflower have not. Why should this be?
The shooting down of the radicle or undeveloped root, and the springing up of the plumule or undeveloped stalk, is accordingly due to no vital principle in the seed, but to the complexity or entanglement of the molecules wrapped up in their integumentary environment.
But there can be no doubt that embryonic, excluding larval characters, are of the highest value for classification, not only with animals but with plants. Thus the main divisions of flowering plants are founded on differences in the embryo on the number and position of the cotyledons, and on the mode of development of the plumule and radicle.
Closely applied to one side of this, so closely that it is difficult to separate it perfectly, is the single cotyledon. This completely surrounds the plumule and furnishes it with food from the albumen. There is a line down the middle, and, if we carefully bend back the edges of the cotyledon, it splits along this line, showing the plumule and caulicle within.
Here is the sweetest longitudinal section of the tentacle of an Actinia, and here look at these lovely transverse sections of the plumule of a pea; you can see the primary groups of spiral vessels. They've taken the carmine stain wonderfully! But my work is not advanced; I wish you could see that of the other girls." "I mustn't interfere with your task; I'll look about until you are ready."
Under these circumstances, unnatural as they are, with proper management, the bean will thrust forth its radicle and its plumule; the former will grow down into roots, the latter grow up into the stem and leaves of a vigorous bean-plant; and this plant will, in due time, flower and produce its crop of beans, just as if it were grown in the garden or in the field.
The last plumule floated away. Winsome Charteris had risen instinctively, and stood looking with crimson cheeks and quicker-coming breath at this young man who came upon her in the nick of time. He was startled and a little indignant.
The same fact holds good with flowering plants, of which the two main divisions have been founded on characters derived from the embryo, on the number and position of the embryonic leaves or cotyledons, and on the mode of development of the plumule and radicle.
But let no man think the vast all-shadowing redwood trees of California grew in a mushroomic night. When the seed first thrust its rootlets down into the soil and its plumule up to the sunshine it entered upon a long career.
A caulicle. The outer covering is the wall of the ovary, the inner the seed-coat. Bean. A seed covering. Two cotyledons. A caulicle. A plumule. Pea. The same as the Bean. They have also learned how the first leaves in the last three differ from those of the Morning-Glory, being considerably thicker in the Sunflower, and very much thicker in the Bean and Pea.
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