212 MORPHOLOGY OF ANGIOSPERMS 



fusion was observed in several parthenogenetic species of Al- 

 chemilla (A. sericata, A. " hybrida" A. pubescens, A. pasto- 

 raliSj A. acutangula, A. alpestris, and A. speciosa), its failure, 

 as in Antennaria alpina, can hardly be regarded as character- 

 istic of parthenogenetic forms. In the parthenogenetic species 

 of Alchemilla, as Antennaria alpina, the number of chromo- 

 somes remains unchanged throughout the life-history. Al- 

 though the number was not positively established, the counting 

 never showed less than thirty-two or more than forty-eight. 

 In Alchemilla arvensis, in which fertilization regularly occurs, 

 the numbers are sixteen and thirty-two. Aside from the more 

 difficult cytological evidence, a convincing proof of the existence 

 of parthenogenesis in Alchemilla alpina is found in the fact 

 that the segmenting embryos are often obtained from unopened 

 buds in which no pollen has been developed.. In A. arvensis 

 (Murbeck 77 ), in which fertilization occurs, the pollen-tube en- 

 ters the chalaza and traverses the integument. 



In 1902 Overton 83 discovered parthenogenesis in Thalic- 

 trum purpurascens, the investigation having been suggested by 

 an early observation that Thalictrum Fendleri set seed freely 

 in the absence of staminate plants. Only ovulate plants were 

 brought into the greenhouse and forced. These set seed con- 

 taining good embryos several weeks before the staminate plants 

 of the vicinity had developed pollen. Investigation showed 

 beyond a peradventure that these embryos were derived from 

 unfertilized eggs. He also compared normal and parthenoge- 

 netic embryos, and found that the latter are noticeably slower 

 in starting, though the two kinds become exactly alike at matu- 

 rity. The cytoplasm is very dense about the unfertilized egg, 

 and w T hen a zone in contact with the egg changes in appear- 

 ance the first segmentation occurs. He suggests that there is 

 a reaction of some kind between the egg and the contiguous 

 cytoplasm that brings about the change in the physical con- 

 stitution of the egg that induces segmentation. This is con- 

 ceivable from the fact that artificial parthenogenesis has been 

 induced in the unfertilized eggs of certain low animals by 

 changing the osmotic pressure. Overton finds that in nature 

 this species probably produces normal and parthenogenetic em- 

 bryos in about equal numbers. 



Still more recently Treub 92 has concluded that Ficus hirta 



