AMIOTIC PARTHENOGENESIS IN TARAXACUM 



VULGARE (LAM.) SCHRK. AND TARAXACUM 



LAEVIGATUM (WILLD.) DC. 



A Preliminary Peport.'" 



Pail B. vSears. 



The work of which the results are here offered, awaiting 

 detailed presentation in a paper to follow, was begun at the 

 University of Nebraska in 1914, under the direction of the 

 late Dr. Cliarles E. Bessey. The two species of dandelion which 

 have been studied are respectively the Leoiitodon taraxacum 

 and the L. crythrospermum of the Second Edition of Britton 

 and Brown's Illustrated Flora: the nomenclature used in the 

 title of this paper has been adopted on the basis of evidence 

 presented in the monograph of the genus Taraxacum by 

 Handel-Mazetti.i 



Both of these species were among the number found by 

 Raunkiaer- to be " parthenogenetic " when he performed his 

 classic castration experiments in 1903. His operation, which 

 consists of removing anthers and stigmas before anthesis, and 

 subsequent protection from pollination, has been frequently 

 and successfully repeated in the case of both species, without 

 affecting the viability of the seeds produced. 



Moreover, the observations of various authors, notably 

 Raunkiaer- and Kirschner\ to the effect that its own pollen is 

 not to be found germinating on the stigmas of T. viilgare, are 

 true for both species investigated, so far as known. Whether 

 or not the pollen of sexual species of dandelion would germinate 

 on the stigmas of either of these forms is not to be ascertained 

 by w^ork here, for such sexual species are unknown in the 

 mid-western United States. 



In both species, to-wit, the grey-fruited and red-fruited 

 dandelions, the development of the embryo-sac has been care- 

 fully studied. The embryo-sac-mother-cell, or megasporocyte, 

 only divides once, forming two daughter cells with the somatic 

 or 2x chromosome content. Juel,"* of course, in 1904, found this 

 to be true of T. vulgare, but I am aware of no similar investiga- 

 tion in the case of T. IcBvigatum. In both species one of the 

 daughter cells degenerates, while the remaining one gives rise 

 to an embryo sac of normal eight-nucleate type, but with 



*Summarizing a paper read before the Ohio Academy of Science, April 21, 1916. 



97 



