418 MORPHOLOGY. 



168. 2. Monocotyledons. In all the plants of this group which 

 I have 'hitherto examined, the embryonal globule, originating in the 

 way above described, is definitely bounded in its entire circum- 

 ference ; where a striking suspensor exists, the apex of the radicle, 

 which has its outline clearly marked, projects into the cavity of the 

 utricle, the remnant of the pollen-tube which is applied around it. 

 Its form varies, sometimes globular, sometimes ovate, with the 

 narrower end turned, as radicle, towards the micropyle. By the 

 constant .operation of the process of cell-formation, it grows, and 

 is composed of successively more numerous and smaller cells. 

 In the Orchidacea alone it persists in the earliest condition until 

 the ripening of the seed and germination ; in all other plants yet 

 investigated, a cotyledon is formed in the following manner. 

 Somewhat laterally to the apex of the embryo (therefore somewhat 

 below it), a little papilla arises; from the base of this papilla a 

 greater amount of the periphery is gradually included as part of 

 the elevation, till at last a leaflet is formed surrounding the apex 

 (terminal bud) with its base. The terminal bud (plumule) then 

 projects like a papilla from the sheath of this leaf, the margins of 

 which (constantly lower from the axis of the leaf toward the angles) 

 are in contact. Thus far the development of all embryos which I 

 have investigated is exactly similar, at most differing in the fact 

 that the portion of the embryo in the lower half of the cotyledon 

 sometimes attains a very considerable size about this time, some- 

 times merely forms the lower end of the embryo, in the shape of a 

 cone rounded off at the apex. All the further, in outward appear- 

 ances such great variations of Monocotyledonous embryos, are 

 dependant on the unequal development of these parts, which are 

 all alike in the rudimentary condition of the radicle (Naiadece and 

 some other families, which L. C. Richard named embryons macro- 

 podes) or of the cotyledon (in Schcuchzeria, most Aracece), &c. 



In spite of the apparently great variation of the embryo in Monocotyle- 

 donous plants, the manifold forms all start from one element, and have the 

 main point of the development in common. The earliest rudiment here, 

 as in the Dicotyledons, the embryonal globule, developes no further up to 

 the period of germination in the Orchidacece (fig. 254.). In all others the 

 changes above mentioned manifest themselves, and a few examples may 

 illustrate the statement, for which purpose the embryo of Potamogeton 



254 



c, the radical extremity, lost in loose cells. B, A somewhat later condition, in which 

 the individual cotyledons are already distinctly recognisable: a, b, c, as in A. 



844 Neottia picta. Ovate embryo, without a cotyledon. 



155 Potamogeton lucens. A, Embryo : a, radicle ; 6, cotyledon. B, Longitudinal 

 section of the same : a, 6, as in A ; c, slit of the cotyledon, with the plumule. 



