762 PHrSIOLOGY. 



division, forms a suspensor (fig. 1115, s), by which the lower cell 

 is suspended from the apex of the embryo-sac. This lower 

 cell assumes commonly a globular form (figs. 1115, r), and 

 ultimately by cell-division forms the embryo, which is either 

 mono- or di-cotyledonous according to the conditions under 

 which it is developed. The suspensor is not present in all cases, 

 while in others in which it is found it varies in its length. It is 

 evidently not essential in all instances, as it always shrivels 

 up during the development of the cell which it supports into 

 the embryo. The latter, therefore, is the true rudimentary em- 

 bryo. Other variations occur in the mode in Avhich the ger- 

 minal vesicle is developed into an embryo, but the above is a 

 general sketch of the subject, and all that our space will allow 

 us to notice. 



The changes which take place in the ovule during the de- 

 velopment of the embryo, and the subsequent growth of the 

 latter, have been already alluded to when treating of the seed. 

 (See Nucleus or Kernel, p. 342 ; and. Development of the 

 Embryo, p. 345.) 



Hybridization, Hybridation, or the Production of Hybrids in 

 Plants. — If the pollen of one species is applied to the stigma of 

 another species of the same genus, should impregnation take 

 place, the seeds thus produced will give rise to oiFspring inter- 

 mediate in their characters between the two parents. Such 

 plants are called hybrids or mules. The true hybrids which are 

 thus produced between two species of the same genus, must not 

 be confounded with simple cross-breeds, which result from the 

 crossing of two varieties of the same species ; these may be 

 termed sub-hybrids. 



As a general rule, true hybrids can only be produced between 

 nearly allied species, although a few exceptions occur, where 

 hybrids have been formed between allied genera ; these are 

 called bigeners. The latter, however, are not so permanent as 

 the former, for in almost all cases they are short-lived. 



Hybrids are always intermediate in their characters between 

 the two parents, but they generally bear more resemblance to 

 one than the other. Sometimes the influence of the male 

 parent is most evident, and at other times that of the female, 

 but no law can at present be laid down with regard to the kinds 

 of influence exerted by the two parents respectively, in deter- 

 mining the characters of the hybrid. In very rare cases, it has 

 been noticed, that ditterent shoots of the same hybrid plant 

 have exhibited diflerent characters, some bearing flowers and 

 leaves like their male parent, others like the female, and some 

 intermediate between the two. In such cases, therefore, the 

 hybrid characters are more or less separated in the diflerent 

 shoots, which present respectively, the characters of one or tlic 

 other of their parents. 



