DEGENERACY OF FLOWERS. 265 



Now, the three genera of Grasses here mentioned are 

 characteristic of warmer regions, and even tropical, Leersia 

 oryzoides being the sole species of that genus which reaches 

 Europe, where it becomes cleistogamous. Therefore climatal 

 conditions may, with some reasonable presumption, be sug- 

 gested as the immediate cause in these cases. With regard to 

 Hordeum murinum, which is, perhaps, almost habitually cleis- 

 togamous in this country, it may be an hereditary result 

 issuing from a similar cause. This may also apply to Viola ; 

 for not only are some species tropical, but all the genera 

 most nearly allied to Viola are tropical also. This is analo- 

 gous to what I have suggested as the origin of gynodicecism 

 in LabiatcB, which it may be noticed has at least two genera 

 with cleistogamous flowers in this country or Europe. Juncus 

 iufonius, according to Batalin, is exclusively cleistogamous 

 in Russia, hence the same cause suggests itself for this 

 species ; for, according to Ascherson, at Halle it has ordinary 

 open, lateral, hexandrous flowers in addition to terminal 

 cleistogamous triandrons ones.* This seems to show that 

 lessened vigour has also a hand in the process in this case : 

 the mean temperature of Halle is probably higher ; if so, it 

 may cause the plant to bear the open flowers there. 



From the above-mentioned facts, it will be seen that 

 there may be more than one cause to account for cleistogamy. 

 Hence, it must be regarded as an inevitable result whenever 

 those influences are brought to bear upon the plant which 

 are capable of producing it ; and there is every reason to 

 believe that whatever effects are produced in plants by 

 external stimuli, if the latter be permanently kept up they 

 will become hereditary, and then will be recognized by 

 systematists as specific or generic characters. 



Anemophilous, oe Wind-feetilised Plants. — The general 



• Muller, he, p. 561. 

 25 



