OF THE ORGANS OF EEFEODUCTION, 765 



equal in size ; hence all irregularity is produced by unequal sub- 

 sequent growth. 



2. Of the Essential Organs of Eeproduction. — SextiaUty 

 of Plants. — Though vaguely suspected by the ancients, the true 

 sexuality of plants was not definitely ascertained till 1676, in 

 ■which year Sir T. Millington, of Oxford, determined the real 

 nature of the stamens. The stamens of flowering plants, as has 

 been already repeatedly stated, constitute the male apparatus, 

 and the carpels the female. That the influence of the pollen is 

 necessary to the formation of perfect seed is positively established 

 in the immense majority of flowering plants ; and although cer- 

 tain apparent exceptions occur, which we flnd it impossible to 

 explain in the present state of our knowledge, where perfect 

 seeds have been produced without the agency of pollen, still such 

 isolated cases must not be allowed to overthrow the great mass 

 of evidence which may be adduced to show, that the pollinic 

 influence is essential to the production of a seed with a perfect 

 embryo. It would appear from various observations, as from the 

 kind of Parthenogenesis which takes place in some plants, that 

 a single impregnation may be sufficient to produce several gene- 

 rations. 



"While the presence of distinct sexes may thus be shown in 

 flowering plants, both of which are necessary for the formation 

 of perfect seed, flowerless plants, in like manner, possess certain 

 organs the functions of which are undoubtedly sexual. It is 

 quite true that the existence of sexuality has not been absolutely 

 demonstrated in all the Cryptogamia ; but as it is known to 

 exist in the greater number, we may fairly conclude from analogy 

 that it is present in all. 



We have just stated that a seed is only to be considered per- 

 fect when it contains an embryo which is capable of germina- 

 ting and producing a new plant; flowerless plants, however, 

 have no true seeds containing an embryo, but are propagated 

 by spores (page 358), which either reproduce the plant directly, 

 or give rise to an intermediate body, called the 2^^othaUmm, jpro- 

 thalhis {fig. 1^1 , p), pro-ernbryo, or frotoncma, from which the 

 fructiferous or fruit-bearing plant ultimately springs (see page 

 361). We can only give a general summary of the more im- 

 portant conclusions which have resulted from researches in this 

 subject. 



1. Reproduction of Ceyptogamoi^s or Acotyxedonoits 

 Plants. — We have already described the structure of the repro- 

 ductive organs of these plants (see pp. 358 — 385), and, in doing 

 so, we treated of them in two divisions, called, respectively, Acro- 

 gens and Thallogens, each of which was again sub-divided into 

 several natural orders. We shall follow the same arrangement 

 in describing their modes of reproduction, except that we shall 



