HOW PLANTS GROW. 229 



plumule during germination. Except this difference, germination 

 is similar in both seeds. Both are Dicotyledons ; indeed, the 

 presence of one or two seed-leaves affects only the morphological, 

 not the physiological aspect of seed-life. 



We see, therefore, that the function of the Cotyledons is one of 

 nourishment. They may perform this in either of two ways. They 

 may simply nourish, and then shrivel up and decay underground, 

 as in Pea, Oak, Chestnut, Orange, and in most Monocotyledons, 

 when they are termed HypogcEous ; or they may be carried up 

 above the ground, acquire chlorophyll under the action of light, 

 becoming green ; then, they feed the plumule, or growing stem, 

 by assimilation, like ordinary leaves. This is seen in Maple, Syca- 

 more, Birch, Beech, Lime, Mustard, and many others ; the host of 

 little two-leaved plantlets, seen covering the ground under a beech- 

 tree in early spring, are these two cotyledons doing their work ; in 

 this case, they are called Epigceous — />., above ground. 



The conditions absolutely essential for germination are only 

 three : heat (above zero), air^ and moisture. Given these three, a 

 seed will germinate. Of course, as a usual thing, it is, in addi- 

 tion, placed in the soil, where its roots can absorb due nutritive 

 materials. Having germinated, how is it to get on until the 

 embryo, now freed from its covering, or Testa^ can set up for itself 

 as an independent organism, and make its way in the world ? 



I St. — The nutrient matter in the albumen, or cotyledons, must 

 be dissolved, that it may nourish at all. It is mostly insoluble, in 

 the form of starch. To remedy this, oxygen is absorbed, car- 

 bonic dioxide being evolved (causing the loss of weight so well 

 known in growing-seeds) ; the starch is changed into dextrine, 

 thence into sugar, some of it being converted into carbonic di- 

 oxide. During this stage, heat is being freely given off. 



2nd. — The nutrient matter must be conveyed to the embryo 

 plant. This is accomplished by the water taken in by the plant 

 dissolving out the dextrine and sugar from their cell-stores, and 

 carrying them to the embryo, which they enter usually at the 

 point where the cotyledons join the axis, travelling therefrom, at 

 first, mostly down to the radicle ; afterwards, both thither and up 

 towards the plumule. 



3rd. — These materials must be changed into the substance out 



