268 OX SEEDLINGS 



species of Cuscuta have an embryo consisting of a terete spiral 

 body with inconspicuous or obsolete cotyledons. A well-marked 

 type of seed occurs in the numerous species of Convolvulus 

 and Ipomcea, and as they correspond pretty closely they may 

 be taken together. "When more than two seeds reach maturity 

 in a capsule, they are bluntly trigonous with the hilum basal, 

 and facing the inner angle of the cell obliquely. The interior 

 of the seeds is remarkable for an invagination of the tegmen 

 along the ventral angle. The extent to which it is infolded 

 varies greatly in different species ; in all cases it is perhaps 

 most marked at the apical end of the seed, and from thence it 

 is continued towards the base. The seeds of some species are 

 almost two- celled owing to the excessive development of this 

 pecuh'ar process, and a small opening is left just sufficient to 

 permit of the embryo pushing half of each cotyledon into 

 each of the halves of the seed. There is also a singular 

 invagination of the micropyle close to the hilum, forming with 

 the dorsal integument of the seed a tubular cavity hi which the 

 embryo arises, and which ultimately accommodates the radicle 

 only. This is not so rare an occurrence as the first mentioned 

 process, as we meet with it hi species belonging to various 

 Orders, although generally it is much less marked. Some- 

 thing like it occurs in Acer and ^Esculus belonging to the 

 Sapindaceae. The embryo is large, and during development 

 the cotyledons grow till they reach the apex of the seed or till 

 they meet the invagination of the tegmen when the growth of 

 the primary axis or midrib is stopped ; or if it continues to 

 grow, then the cotyledons become folded transversely upon 

 themselves in the dorsal region of the seed. Sooner or later 

 however the cotyledons become concave on the ventral aspect, 

 and obliquely lateral lobes are developed so as to occupy the 

 cells on each side of the invaginated tegmen. This causes 

 the cotyledons to become emarginate, bifid or bipartite 

 according to the length of the lateral lobes. "When the latter 

 attain great length they become very much folded, plicate or 

 crumpled, giving the cotyledons the characteristics which mark 

 them after germination. "When the seeds are large and the 

 cotyledons but little folded, the latter are but shallowly bifid 

 or merely ernarginate after germination ; but when the seeds 



