572 OX SEEDLINGS 



other end remains in the seed. The cotyledon thus consists 

 of a short lower sheathing portion, from which the second 

 leaf soon breaks in the form of a long, slender, wedge-like 

 sheath with a green tip, and an upper portion perfectly con- 

 tinuous with it hi connection with the seed, its apex remaining 

 embedded in the endosperm. This is the simplest type. We 

 have represented, in what is evidently a single structure, the 

 cotyledon, first an absorbent organ to absorb the endosperm 

 contained in the seed ; secondly a means of connection between 

 this and the seedling ; and thirdly a protecting sheath for the 

 developing plumule. 



In the second type, the more general one in the Order, the 

 cotyledon shows greater differentiation of structure, the parts 

 which perform the three functions being quite distinct from 

 each other. The lower portion still forms the protecting 

 sheath, but is much longer than in the first type. Attached 

 to it, either at the apex, or some varying distance below, is a 

 long thread-like connective, the other end of which is swollen 

 into a more or less club-shaped absorbent organ, buried in the 

 endosperm of the seed. As in the first type the whole of the 

 cotyledon remains beneath the ground. This obtains, accord- 

 ing to Irraisch, in Iris sibirica and I. Xiphion, 1 and probably 

 in many other species, also in Gladiolus communis, palustris, 

 and other species. Alefeld 2 says a Morsea germinated just 

 like Iris. 



The third type differs in that the long thread-like coty- 

 ledon after exhausting the endosperm gets quite free from the 

 seed and appears above the soil as the first green foliage-leaf. 

 Hence the striking differentiation of structure of the last type 

 is absent. The hypocotyl, as general in the Order, is un- 

 developed. Germination begins with the elongation of the 

 lower part of the cotyledon, which pushes the root before it, 

 and follows it, both growing quickly, a short distance down- 

 wards in the soil. Rapid growth at the bend causes the coty- 

 ledon to form a sharp knee, and each of the two limbs 

 continuing to grow, this is pushed upwards, thus breaking the 

 soil in the manner of the hypocotyl of many Dicotyledons. 



1 Abhandl. Nat. Ver. Sachs, u. Thuring. Halle, i. p. 139. 

 2 Alefeld, Bat. Zeit., 1864, p. 246. 



