466 



PARTHENOGENESIS. 



pointed out that many female plants of Mercurialis annua bear here and there 

 a male flower alongside the female ones. For the refutation of these objections 

 fresh experiments were necessary in which every precaution should be exercised 

 to eliminate sources of error. Such espeiiments should be conducted in some 

 district in which for miles around the plant did not grow wild, so that the possi- 

 bility of casual introduction of pollen might be excluded. Fulfilling this require- 

 ment is the Central Tyrol, from which both the annual and perennial species 

 of Dog's Mercury are absent. Accordingly I repeated in my upland garden in 

 the Tyrolese Gschnitzthal the cultural experiments originally carried out in 1833 

 by Ramisch at Prague. Every precaution was taken to avoid sources of error; 



Fig. 345.— The Annual Dog's Mercury {Mercurialis annua). 

 1 With male fluwers 2 With female flowers. 



«.nd in particular were all plants destroyed which showed a tendency to produce 

 male Howers, and the utmost vigilance kept lest an isolated male or hermaphrodite 

 flower should make its appearance anywhere. At the time when the stigmas 

 were ready to be pollinated there were no pollen-grains of this plant anywhere 

 in the neighbourhood for miles around, so that the possibility of such a pollination 

 was excluded. Nevertheless the ovaries set and fruit was ripened, and from the 

 seeds young plants arose. 



Another plant, also belonging to the Euphorbiacete, in which embryos arise 

 in unfertilized ovules, is Cosiebogyne ilicifolia. It was introduced into Eurojje 

 from the bush of Eastei-n Australia in 1829, and is now in general cultivation 

 as a hot-house plant in Botanic Gardens. The first specimen introduced bore only 

 female flowers, and all the plants which have been raised from this specimen, anil 

 distributed over Europe, re.semble it in this respect. Plants of Gadehogyne with 

 male flowers are unknown in European conservatories. The possibility of such 



