1859.] MONCECIOUS AND DlffiCIOUS PLANTS. 259 



In the * Gardeners' Chronicle/ 1851, is an' account and figure 

 of a monoecious "Hop, and the writer, Mr. Masters, of Canter- 

 bury, therein states that in his own garden he has known an 

 instance wherein a hop-plant has, after producing female blos- 

 soms only, in the next year produced both male and female, and 

 in the folloAving year male flowers only. 



We are not entirely without evidence as to the effect of 

 temperature on unisexual flowers. Thus Nolte, of Copenhagen, 

 states that Stratiotes aloides, which extends from 48° to 68 

 of latitude, produces perfect flowers only between 52° and 53° : 

 north of that, female flowers alone are met with ; south of that, 

 males alone. 



This plant is one which, as is well known, increases rapidly 

 by o9"-shoots. This is in accordance with the observation of 

 Knight, that a high temperature favours the formation of 

 stamens; a low one that of pistils. That accurate observer 

 found this to be the case in the Water-Melon, Cucumber, and 

 other plants. In this country Honckenya peploides is dioecious, 

 in America it is not so, according to Dr. Gray. 



Mr. Hampe observed in Salix repens, that twigs above the 

 water blossomed as females, whilst those twigs that had been in 

 the water, and subsequently blossomed when the water was 

 dried iip, had only male blossoms. (Linnsea, vol. xiv. p. 367.) 



But there are other and still more striking facts lately dis- 

 covered which throw much light on the distribution of the sexes 

 in dioecious plants, by showing that the presence of the pollen is 

 not in all cases necessary to ensure the formation of the embryo. 

 Thus Radlkofer has submitted to renewed examination the 

 Coelebogyne at Kew, a female plant which year after year has 

 produced seeds without possible contact of pollen. In this plant 

 Radlkofer has traced some stages of the development of the 

 embryo, but has not been able to detect any trace of pollen. 



Naudin also has observed the like phenomena in Hemp, IMer- 

 cury, and Bryonia, where all precautions to exclude pollen have 

 been taken. 



These facts are analogous to what has been found to be the 

 case in bees and butterflies by Siebold and other naturalists. 



