334 



PAETS OF THE EMBKYO PLANT. 



small cavity in the centre of the cells, and radiating spaces uncovered 

 with thickening matter, is well seen under the microscope. 



The embryo consists of cotyledons or rudimentary leaves, the 

 'plumule (plumula, a little feather), or gemmule (gemma, a bud), repre- 

 senting the ascending axis, radicle (radix, root), or the descending 

 axis, and their point of union the collum, collar or neck ; that part of 



Othe axis which intervenes between the collar and cotyledons 

 being the caulicule (cauliculus, a little stalk), or tigelle (tigellus, 

 a little stalk). The embryo varies in its structure in the dif- 

 Fig. 594. ferent divisions of the vegetable kingdom. In acrogenous and 

 thallogenous plants it continues as a cell or spore, with granular matter 

 in its interior (fig. 594), without any separation of parts or the produc- 



Fig. 696. 



Fig. 696. 



Fig. 597. 



tion of cotyledons. Hence these plants are called acotyledonous (ol privar 

 tive, %orDX>)5w»). Endogenous and Exogenous plants, on the other hand, 

 exhibit a marked separation of parts in their embryo, the former 

 having one cotyledon, and hence being monocotyledonous (//lovog, one) ; 

 the latter two, and hence dicotyledonous (Sis, twice). Thus, the 

 whole vegetable kingdom is divided into three Classes Ijy the nature 

 of the embryo, the first of which classes corresponds with the 

 cryptogamic division of plants, the second with the endogenous 

 division of phanerogamous or flowering plants, the third with the 

 exogenous division of the same. Fig. 595 represents a monocotyle- 

 donous embryo, with its cotyledon, c; while figs. 596 and 597 exhibit 

 a dicotyledonous embryo, with its cotyledons, c c. 



The Spore of acotyledonous plants (fig. 594) is a cellular body. 



Fig. -694. Acotyledonous embryo of Marchantia polymorplia. Such embryos bear the 

 Dame of spores. Fig. 595. Monocotyledonous embryo of Potamogeton perfoliatus nearly 

 mature, r, Radicle, t, Caulicule or tigellus. c, Cotyledon, g, Gemmule or plumule. 

 Fig. 696. Mature dicotyledonous embryo of the common Almond, r, Radicle or young 

 root. Fig. 597. The same, with one of the cotyledons removed, r. Radicle, t, Tigelle or 

 caulicule. c, One of the cotyledons left, ic. Cicatrix left at the place where the other 

 cotyledon was attached, g, Gemmule composed of several smaU leaves. 



