Darling: Sex in dioecious plants 181 



noteworthy investigations on dioecious flowering plants, he 



believes, warrant the 



) 



sex tendency which is female. (2) In each microsporangium two 

 kinds of pollen spores are formed in equal number ; half having the 

 tendency to develop staminate individuals and half to develop 

 pistillate individuals. (3) The staminate tendency dominates the 

 pistillate tendency. 



Noll ('07) in his work on the dioecious Cannabis has been led 

 practically to the same conclusions as those of Correns, and inde- 

 pendently of the latter's results. It has been known for some 

 time from the observations of Heyer, Haberlandt, and Strasburger 

 that in a state of nature the distribution of staminate and pistillate 

 plants in the dioecious forms is nearly equal. Heyer found, after 

 observations on several thousand individuals, that in Merciirialis 

 annua the proportion was 106 staminate to 100 pistillate ; in the 

 same species Strasburger found the ratio to be 103.8 staminate to 

 100 pistillate, and in Melandrmm album he found 100 staminate to 

 128,16 pistillate. In Cannabis^ Heyer found from 40,000 plants 

 the proportion to be 100 to 11 4. 93 ; Haberlandt in Austria in the 

 same species found 100 staminate to 120.4 pistillate; and Fisch in 

 Erlangen found from 66,000 plants I GO staminate to 1 54.24 

 pistillate. To determine the cause of this ratio, Noll first gathered 

 seeds from various individual plants of Cannabis which had been 

 pollinated by natural agencies. On growing these seeds he found 

 that the percentage of staminate and pistillate offspring derived 

 from the seeds of a single plant varied materially from the normal 

 ratio. In some extreme cases only 10 per cent, were pistillate, 

 while in other extreme cases 90 per cent, were pistillate ; it should 

 be stated that in general there was no such extreme variation. 

 From this evidence he concludes that the ^g% does not determine 

 the ratio, otherwise there would not be such extremes of variation. 



In the second place he crossed individual pistillate plants with 

 the pollen from a single anther, with the result that the ratio of the 

 offspring showed a very close approximation to the normal. From 

 a plant crossed with pollen from a single anther there were obtained 

 100 staminate and 117. 3 pistillate, while from a plant crossed with 

 the pollen from a single inflorescence there resulted 100 staminate 

 and 1 2 1.6 pistillate. Noll was led to believe from these experi- 



