274 



MANUAL OP BOTANY 



(b) The Dicotyledonous Embryo. — These embryos vary 

 very much in form : most frequently they are more or less oval, 

 as in the Bean and Almond (fig. 594), where the embryo con- 

 sists of two nearly equal cotyledons, c, between which is en- 

 closed a small axis or ligeJluvi, t, the upper part of which, g, is 

 the plumule, and the lower, r, the radicle. The tigellum upon 

 germination appears as a little stalk, supporting the cotyledons, 

 and hence it is also termed the hypocotyledonary axis, or 

 hypocotyl. 



In by far the majority of cases the two cotyledons are nearly 

 of equal size, as in the Pea {fig. 16, c, c), but in some embryos, 

 as in Trajpa, some Hircaas, &c. (fig. 595, c', c), they are very 



Fig. 594. 



-Fig. 597. 



FlC4. o95. 



FiGt. 596. 



Fiii. 594. Tlie embryo of tlie Almond (Prt/nus Amygdalus), from which 

 one of the cotyledons has been removed, c. The cotyledon which has 

 been left. r. Radicle, g. Plumule, t. Tigellum. c'. Scar left by the 



removal of the other cotyledon. /%. 595. Vertical section of the 



embryo of a species of Bircea. c'. Large cotyledon, c. Small cotyledon. 



g. Plumule, r. Radicle. Fig. 596. Vertical section of the embryo of 



Carapa gmanensis, showing the almost complete union of the cotyledons, 



the line, c, only dividing them. r. Radicle, g. Plumule. Fig. 597. The 



embryo of Pekea hutyrosa. L Large tigellum. c. Rudimentary cotyle- 

 dons. 



unequal. Again, while the cotyledons usually form the greater 

 part of the embryo (fig. 16, ( , c), in other instances, as in PeJcea 

 hutyrosa (fig. 597, c), they form but a small portion. In Carapa 

 (fig. 596), again, the two cotyledons become united more or less 

 completely into one body, so that the embryo appears to be 

 monoootyledonous ; but its nature is readily ascertained by the 

 different position of the plumule in the two cases ; in the 

 monocotyledonous embryo the plumule is situated laterally 

 (fig. 591, p) ; but here (fig. 596, g) it is between the cotyledons. 

 The cotyledons are sometimes altogether absent, as in Cuscuta. 

 (c) The Polycotyledonous Embryo. — In the Gymnosperms, 

 as already mentioned, there are often several cotyledons, and 



