HOW PLANTS OBTAIN THEIR FOOD. IO7 



of this plant we would not recognize it. It is simple, that is it 

 consists of one lamina or blade, and not of three leaflets as in 

 the compound leaf of the mature plant. The simple leaf is 

 ovate and with a broad heart-shaped base. The jack-in-the- 

 pulpit, then, as trillium, and some other monocotyledonous 

 plants which have compound leaves on the mature plants, have 

 simple leaves during embryonic development. The ancestral 

 monocotyledons are supposed to have had simple leaves. Thus 

 there is in the embryonic development of the jack-in-the-pulpit, 

 and others with compound leaves, a sort of recapitulation of the 

 evolutionary history of the leaf in these forms. 



216a. Germination of the pea. Compare with the bean. 

 Note especially that the cotyledons are not lifted above the soil 

 as in the beans. Compare germination of acorns. 



Digestion. 



2166. To test for food substance in the seedlings studied. The pumpkin, 

 squash, and castor-oil bean are examples of what are called oily seeds, though 

 flaxseed, cotton-seed, and nuts are better. Remove a small portion of the 

 substance from the cotyledon of the squash and crush it on a glass slip in 

 a drop or two of osmic acid.* Put on a cover-glass and examine with the 

 microscope. The black amorphous matter shows the presence of oil in the 

 protoplasm. The small bodies which are stained yellow are aleurone 

 grains, a form of protein or albuminous substance. Make sections of the 

 meat of a Brazil nut or hickory nut and immerse for several hours in osmic 

 acid. They become black because of the quantity of oil. Mount in 

 water and examine under the microscope. The oil is in globules which 

 are colored black. The oil is converted into an available food form by 

 the action of an enzyme called lipase, which splits up the fatty oil into 

 glucose and other substances. Lipase has been found in the endosperm of 

 the castor bean, cocoanut, and in the cotyledons of the pumpkin, as well 

 as in other seeds containing oil as a stored product. The aleurone is made 

 a\ailable by an enzyme of the nature of trypsin. 



Test the cotyledon of the bean with iodine for the presence of starch. If 

 the endosperm of corn seed has not been tested do so now w.th iodine. 

 The endosperm consists largely of starch. The starch is converted to glu- 



* Dissolve a half gram of osmic acid in 50 cc. of water and keep tightl) 

 corked when not using. 



