398 



MORPHOLOGY. 



One of the rarest phenomena is that in which the formation of the 

 outer integument begins higher up upon the seed-bud than the inner, 

 so that the upper half of the nucleus is covered with two integuments, 

 and the lower part only by a very thick, simple one, as is the case in the 

 Tropaolacece (fig. 248.). A similar result occurs in Ricinus (fig. 249.) 



249 



248 



through the opposite process : here the outer integument commences 

 much lower down than the inner one, and the upper part of the seed-bud 

 exhibits two integuments, the under part only one, which is the external 

 one. 



In the presence of integuments, the relation of the chalaza to the rest 

 of the seed-bud, which consists of nucleus and coats, varies exceedingly. 

 The chalaza is usually confined to a small point at the base of the ovate 

 nucleus ; in the conical nucleus it occupies a greater portion, and in some 

 plants ( Canna), and even some families ( CompositcB\ 

 it takes up half, or more than the half, of the entire 20 



seed-bud. 



Lastly, it is to be mentioned, that on reversed 

 seed-buds a peculiar cellular growth, termed a crista, 

 is not unfrequently developed upon the raphe ; it 

 is sometimes narrow, resembling a cock's comb, 

 as in the species of Corydalis (fig. 250.), sometimes 

 thick and broad, so that the seed-bud itself appears 

 but as a small appendage, as in Aristolochia. Some- 

 times, also, such a growth is formed like a collar 

 around the entire seed-bud, or a part of its basis, as 

 in Hellenia. Again, the funiculus has here and there sometimes peculiar 

 hairy appendages, which often envelope the entire seed-bud, and almost 

 always reach to the micropyle. 



162. The structure of the seed-bud is very simple ; it con- 

 sists of parenchyma and a distinct epithelium ; this latter alone, as a 

 mere fold, frequently forms the inner integument, probably in 



c, embryo-sac ; d, inner, and /, outer integument ; g, micropyle, swollen ; h, chalaza ; 

 r, raphe. 



8-18 Chymocarpus pentaphyllns. Seed-bud in longitudinal section, some time before 

 impregnation, a, Hilum; 6, nucleus ; c, embryo-sac ; d, inner, and f, outer integu- 

 ment ; ff, micropyle ; h, chalaza ; r, raphe. 



249 Hicinus leucocarpus. Seed-bud in longitudinal section, a, Hilum ; b, nucleus ; 

 c, embryo-sac ; d, inner, and /, outer integument ; g, micropyle ; h, chalaza ; r, raphe. 



850 Sanguinaria canadensis. Seed-bud in longitudinal section, some time after im- 

 pregnation, a, Hilum ; b, nucleus ; c, embryo-sac ; d, inner, and f, outer integument ; 

 g, micropyle ; A, chalaza ; r, raphe, with a crest-like excrescence. 



