wees 
RA 
Io4 tructural and Physiological Botany. 
and sweet chestnut, while in other Dicotyledons, as the | 
beech, birch, and lime, they emerge from the soil. The 
plumule of Monocotyledons consists of 
superimposed leaves of a sheath-like or 
cornet-like character (Fig. 368) ; while in 
Dicotyledons the cotyledons, when they 
separate, are green and leaf-lke. 
In all modes of reproduction the pro-. 
perties of the parent plant are transmitted 
to its descendants. When reproduction 
is effected by asexual cells, this is alto- 
gether the case ; but when the reproduc- 
tive cells are fertilised oospheres, only so 
ne ee. far as to maintain the character of the 
eas iG the two species. When the fertilising (male) and 
cotyledons which aoe } 
have risenabove the the fertilised (female) cell are derived from _ 
soil, the testa @ not i : ; 
being yetcompletely plants which belong to different species, 
thrown off. (x 4.) ae ; ° | 
fertilisation can take place only if the 
two species are very nearly related to one another. An 
individual resulting from impregnation of this character is 
a hybrid; and it is determined by a number of circum- 
stances, some of which are still unknown, which of the two 
parent species the hybrid most nearly resembles. Hybrids 
resulting in this manner from the crossing of two species, 
not unfrequently occur in nature; but their power of 
propagation is commonly defective, and they are often 
altogether infertile. 
In systematic botany hybrids are distinguished by names com- 
pounded of those of their parent-species, the name being placed first of 
the one which it most resembles, Thus between Mentha rotundifolia 
and MW. sylvestris, two hybrids are known, JZ. rotundzfolio-sylvestris 
and M. sylvestrt-rotunadtfolia, the former of which most nearly resembles _ 
M. rotundifolia, the later M. sylvestris.» 
1 {A more usual and preferable practice is to place the name of the 
male parent first, of the female parent last. Thus Alentha rotundifolio- 
sylvestris would be the result of the fertilisation of AZ, sylvestris by MM. 
