BEAKING OF THE NEW FACTS. 297 



leaf-bud is developed imder one set of conditions, and a 

 flower under another set ; or as only germ-cells are deve- 

 loped in one plant, sperm-cells in another, or both on the 

 same plant. 



Of great importance as regards the theory of Partheno- 

 genesis are two of the facts just indicated ; namely, that 

 the Polype produces ova which become Medusae ; and 

 that these ova may indifferently become either Polypes oi' 

 Medusfe. The latter fact ceases to be so marvellous, when 

 we consider that Agassiz has demonstrated the identity in 

 structure of Polype and Medusa. 



Of still greater importance as regards the theory of Par- 

 thenogenesis is the conclusion that from germ-cells only, 

 without any influence from sperm-cells. Polypes and Medusae 

 may be developed. Do you ask for evidence on which to 

 base this conclusion ? The evidence is various. "We have 

 already noted the indubitable fact that the unfertilised eggs 

 of Entomostraca, gall-flies, bees, moths, and silk-worms, 

 do become developed animals ; these must spring from 

 germ-cells only. Next we have the recent experiments in 

 France and Gennany, which place beyond a doul)t that 

 dioecious plants become fertile when their pollen is entirely 

 removed ; and we know that female plants become fertile 

 when no pollen-bearing plant is in the kingdom ; so that 

 Schleiden, in the edition of his work. The Plant, just 

 issued, says, " We must now confess complete ignorance 

 as to the real function of the pollen." * To these may 



* Schleiden, Die Pflanze, 1858, p. 72. He draws the piquant conclusion 

 that it is precisely in those plants on which LinnsDus founded his sexual 



