liESEHVE CELLirLOSE. I7 



cotyledon. At 3 the cells are neiirly empty, and all tlie reserve cellulose is exiiausted. 

 At 4 there is some reserve cellulose, which is gradually being removed; the cells still 

 contain oil and protein matters. The outermost cells have been scarcely affecte<l. 



This process, which has been outlined, goes on until all the nourishment has been 

 absorbed from the endosperm, the cotyledon acting as agent of absorption and transfer. 

 The visible chain of processes is reserve cellulose, then oil in the endosperm ; and in the 

 cotyledon, oil and starch. In the young plant the sujiplied material is used up and 

 growth ensues. 



If sugar is formed, and traces of it are certainly to be found in the cotyledon, it is 

 carried over at once into some other compound. 



Germination of Irix pseudacorns. 



Seeds of Iris 2)sendacorus, which were gathered Oct. 1, 1892, were soaked four 

 days and on April 28, 1894, were planteil. After 20 days, on May 18, they had api)eared 

 above the soil, the largest being then three foiu'ths of an inch high. The examination 

 of the unsprouted seed shows, as in Polygonatum, a minute embryo imbedded in endo- 

 sperm, whose cells are hard and firm, the walls being encrusted with reserve cellulose. 

 Through the imbibition of water, the cell walls are slightly swollen and the tissue soft- 

 ened. No other change has taken place since the seed was placed in the ground. The 

 embryo consists of a sheathing cotyledon, whicli encloses the young bud, and of a, minute 

 hypocotyl. 



The method of growth is as follows. The growth of the sheathing petiole of the 

 cotyledon carries the hj'pocotyl and enclosed bud out of the seed. The root grows 

 vigorously downward, and the hypocotylary stem upward, to carry the protected bud 

 above the soil. At the same time, the stem of the cotyledon keeps pace with this growth 

 so that the seed may not be carried up as well. A sharp bend is made by the petiole 

 of the cotyledon, like an elbow joint; one part reaches down to the seed, the (jther, 

 serving as protection for the l)ud, is united below to the steui. The upward growth 

 of the stem and that part of the cotylediju ne.xt it, always corresponds to the growtii 

 of the other arm, which reaches to the seed, so that the seed always remains iu tlie soil 

 at the level of the neck of the root, and the elbow becoming hard and horny serves to 

 make a way through the soil. When above the ground, the sliarply-jjointed end of the 

 first leaf cuts through the sheath. 



PL 4, fig. 1, A, shows a young plant of Iris pseudacorux:, twenty-live days after the 

 sowing of the seed; a, seed with thick testa; b, petiole of the cotyledon ; c, horny tip 

 of the same; d, sheathing portion of the same; e, hypocotylary stem ; f, root; fj, lirst 



