PARTHENOGENESIS. 465 



cases of parthenogenesis, cases, that is, of egg-cells which continue their develop- 

 ment unfertilized. 



Amongst Flowering Plants, also, cases are known in which ovules sometimes, 

 without ever being fertilized, form embryos which grow up into healthy plants. 

 An instructive example is the case of Gnaphalium alpinum { = A'ntennaria 

 alpina), a perennial Composite nearly allied to both the common Cat's-foot 

 (Onaphalium dioicum) and Gnaphalium carpaticum of the Alps and Car- 

 pathians. This plant occurs in Scandinavia from Telemarken to Havosund (59° 

 52' to 71° north, lat.), and in Russia from Finland to the Kola Peninsula, also 

 in Arctic Siberia, in Arctic America, in Labrador, Melville Peninsula and the 

 whole Arctic Archipelago, in Greenland between the parallels 60° and 72° north 

 lat., finally in Iceland. Thus it is distributed in a zone surrounding the North 

 Pole, some 12° in breadth. It is absent from the mountains of Central and 

 Southern Europe, and is not known to exist, for certain, on the mountains of 

 Central Asia. In these northern latitudes Gnaphalium alpinum, is exceedingly 

 common, occurring abundantly in innumerable localities. But it is a remarkable 

 fact that neither in Arctic America nor in Arctic Asia has a plant producing 

 pollen ever been found. In the Scandinavian Flora once, in the year 1842, a 

 pollen-bearing plant was alleged to have been discovered; but this has been dis- 

 credited. A large number of Botanists, thoroughly familiar with the Scandinavian 

 Flora, are unanimous in saying that they have never seen stamen-bearing flowers, 

 and that ovaries only occur. I have myself obtained plants of Gnaphaliuin 

 alpinum from the Dovrefjeld in Norway, and have flowered them in my garden. 

 Every flower produced an ovary but no pollen, so that the possibility of pollination 

 was excluded. A number of achenes ripened containing good seeds, and these, 

 carefully cultivated, produced plants, in all respects similar to the parent form. 

 When these young plants flowered the same phenomena occurred. Thus, one has 

 good grounds for asserting that Gnaphalium alpinum,, throughout the wide area 

 of its distribution, is propagated parthenogenetically, and that its reproduction is 

 not hindered by the absence of pollen-bearing plants. 



Another plant, of which it has been long known that embryos arise in its 



unfertilized ovules, is a species of Dog's Mercury (Mercurialis annua, see fig. 345), 



one of the Euphorbiacese, widely distributed in fields and gardens, in hedge-backs 



and waste places, throughout Central Europe. Some individuals of this species 



produce staminal flowers only (fig. 345 ^), others, female flowers only (fig. 345 ^). 



Its dust-like pollen is conveyed to the stigmas by currents of air, and the ovaries 



of the female flowers ripen seeds freely as the outcome of fertilization. But 



female plants have often been cultivated in pots by themselves, with the result 



that they also ripened seed, though smaller in amount than when there is access 



to pollen, as is the case with plants growing freely in the open. These results 



were much canvassed, and discredit thrown upon them by many. It was urged 



that the dust-like pollen might have come from afar, in the air, and have entered 



the conservatory in which the experiments were conducted; and again it was 

 Vol. n. 80 



