268 Causes and Course of Organic Evolution 



lines of stereoenergizing attraction, which may cause cellulose 

 walls to be molded in shape, or may cause ferments to be exuded 

 that break down the walls at definite areas, or cause lines of 

 movement in the entire cell-masses, so that these are equally 

 attracted to each other (Desmidece, Staurospermiim); or one 

 of the cell-masses so preponderates in its stereoenergesis that 

 it draws the other mass to it. 



But a third and very important peculiarity hinted at above, 

 and almost of necessity bound up with the first peculiarity, 

 is much better known to us as yet amongst higher plants and 

 most animals. This is the evident reduction, disappearance, 

 or absorption, m each conjugating cell, of approximately half 

 its hereditary characters, and this at some period anterior 

 to the fusion of the two cells. For in no other manner can 

 we explain the retention of parental characters typical of both 

 parents, and yet the development of a new plant that is not 

 double the size or vigor or structural detail compared with 

 either parent, but that is a fair average between both. Such 

 reduction has been widely and satisfactorily demonstrated, 

 from some of the higher algse up to the higher flowering plants. 

 The strong probability then is that it will yet be demonstrated 

 to occur in the above simple algae. 



Reference has already been made (p. 264) to the effect of 

 environal agents in promoting continued cell division. But 

 certain agents seem at times to promote, at times to inhibit 

 sex differentiation. Oltmanns has admirably synopsized (99, 2: 

 249-262) the experimental results already obtained. He shows 

 that changes in temperature, in light intensity, in chemical 

 nature of the environal liquid, in stillness or motion of the 

 water, may so influence many algae as to quickly promote or 

 completely retard the formation of sex-cells. 



Another indicative suggestion that many of these plants 

 are still in a state of wavering and evolving sex differentiation 

 is yielded by the numerous recorded examples of partheno- 

 genesis, as well as by the ease with which gamete cells may be 

 modifled by environal agents, so as to become parthenogenetic 

 in their future history Thus Oltmanns (99,2:^55) says: 



