PARTHENOGENESIS 187 



Parthenogenesis is common in plants. There is a lowly 

 fresh-water alga called Chara crinita whose egg develops 

 without union with an antherozoid. In fact, in Europe, where 

 it flourishes, only female plants of the species are known, so 

 there is no chance of fertilization. Many flowering plants 

 produce parthenogenetically. This is perhaps especially true 

 of cultivated plants such as the Compositae (daisies, etc.), 

 members of the rose family, buttercups, thymes, stinging- 

 nettles and many other plants. In these the naked ovum in 

 the embryo-sac develops into the new plant without being 

 fertilized by what corresponds to the antherozoid in the 

 pollen-tube. 



After a queen-bee has been paired high up in the air she 

 returns to the hive with no less than 200,000,000 spermatozoa 

 in her body, a supply equal even to her prodigious fecundity, 

 for she will lay 2500 to 3000 eggs every twenty-four hours, 

 during three or four years. The eggs which are destined to 

 produce the queen and the workers are fertilized, but, by some 

 marvellous arrangement which is not yet fully understood, 

 the spermatozoa are kept back from the eggs destined to form 

 the males or drones, the males being born parthenogenetically. 



Amongst the Rotifera parthenogenesis is very common, 

 especially during the summer months; fertilized eggs appear 

 in the autumn but they are known as winter or resting eggs. 

 They are capable of resisting adverse circumstances and carry 

 on the life of the race during the winter. But in many Roti- 

 fera no male has ever been found and presumably these 

 forms are entirely parthenogenetic. 



Parthenogenesis also occurs in the life-history of many of 

 the lower Crustacea. Both in the Phyllopoda and in the 

 OsTRACODA unfertilized eggs are produced. Here again in 

 some cases males are totally unknown, but in others the male 

 does appear towards the autumn ; the eggs it then fertilizes 

 pass into a resting stage and are protected by a capsule 

 formed by the skeleton of the mother. In many cases males 

 are very rare, sometimes only one per cent, of the total stock. 

 In many insects a similar state of things prevails and there 

 may be here, as among the lower Crustacea, many partheno- 

 genetic generations before the male reappears. 



