GERMINATION. 789 



1. Monocotyledoious Germination. — The seeds of Monoeotyle- 

 donous plants, in by far the majority of instances, contain 

 albumen. This, as the embryo developes, is usually entirely 

 absorbed ; but in the seed of Vhytelephas, the contents of the con- 

 stituent cells are removed, and the walls left as a kind of skeleton. 

 The single cotyledon of Monocotyledonous seeds, when they 

 contain albumen, always remains entirely {fig. 745, c), or par- 

 tially within the integuments, during germination. The intra- 

 seminal portion of the cotyledon corresponds to the limb of 

 the cotyledonary leaf, and the portion which elongates beyond 

 the integuments (extra-seminal) represents the petiolar portion. 

 The latter part varies much in length, and is commonly ter- 

 minated by a sheath, which encloses the young axis with the 

 plumule. In the Palms this petiolar portion is often several 

 inches in length. At other times, there is no evident petiolar 

 part, but the sheathing portion enveloping the axis remains 

 sessile on the outside of the seed, and elongates in a tangential 

 direction to it, as in the Oat {fig. 745), where the cotyledon, c, 

 remains within the seed, and the plimaule, g, rises upwards from 

 its axil, into the air. 



In some few Monocotyledonous Orders, such as Naiadaceae, 

 Alismaeeae, &c., where the seeds are exalbuminous, the cotjde- 

 don is commonly freed from the integuments, and raised up- 

 wards with the plumule. 



As already noticed (p. 121), in the germination of many Mono- 

 cotyledonous embryos, e. g. the grasses, the radicle is not itself 

 continued downwards so as to form the root, but it gives off one 

 or more branches of nearly equal size, which separately pierce its 

 extremity, and become the rootlets {fig. I^b^ r). Each of these 

 rootlets, at the point where it pierces the radicular extremity, 

 is surrounded by a cellular sheath termed the coleorhiza {fi^g. 

 74:5, co). This mode of germination is commonly termed 

 endorMzal : but it is by no means universal in the class. 



2. Dicotyledono^is G-crmination. — The seeds of Dicotyledo- 

 nous plants are either albuminous or exalbuminous, and their 

 germination in such respects, as a general rule, presents no 

 peculiarity worth notice. The two cotyledons either remain 

 within the integuments of the seed as tleshy lobes, as in the 

 Horse-chestnut and Oak, in which case they are said to be 

 hypogeal (from two Greek words signifying under the earth) ; 

 or, as is more commonly the case, they burst through the coats, 

 and rise out of the ground in the form of green leaves {fig. 15, 

 c, c), in which case they are epigml (from two Greek words 

 signifying upon or above the earth). In the course of develop- 

 ment, the cotyledons commonly separate, and the plumule comes 

 out from between them {figs. 14, n, and 15). In those cases 

 where they remain within the integuments, they sometimes be- 

 come more or less united, so that the embryo resembles tliat of 



