86 THE SHORTER SCIENTIFIC PAPERS 



in reality the young individuals — of the common fila- 

 mentous green alga Spirogyra in f lata ( Vauch) . Upon 

 applying statistical methods the close-bred zygospores 

 were found to be 23 per cent more variable^ in size as well 

 as larger, both in length and actual volume, than the cross- 

 bred zygospores. The results were not in accord with 

 the general belief that cross breeding increased variability, 

 although studies by Warren, Kellogg, Casteel and Phillips 

 had pointed out that this belief was not substantiated by 

 facts, which, however, did not actually warrant the idea 

 that variability was decreased in cross-bred forms. The 

 studies on the zygospores also suggested that sex existed 

 primarily for the purpose of limiting variability, a hy- 

 pothesis proposed on purely theoretical grounds by 

 Hatschek in 1887. Another conclusion which followed 

 from the same investigation was that in connection with 

 the origin of death^ and which may be mentioned here. 

 This is summarized by stating that death apparently 

 occurs as the result of the continually forming body cells 

 becoming so variable through absence of control by 

 amphimixis, that eventually some one group of functional 

 importance fails to meet the limits imposed by the envir- 

 onment. In consequence of this the group, together with 

 the remainder of the colony — the individual — perishes. 



In connection with the difference in the variability of 

 close-bred and cross-bred zygospores it seems quite evident 

 that the result is brought about by some factor other than 

 the environmental stimuli which are assumed to produce 

 fluctuation, inasmuch as the material was homogeneous in 

 every respect with the exception of the manner of repro- 

 duction. The question is a difficult one, however, not to 

 be settled by a single investigation giving positive results, 

 and because of its importance should receive attention. 



In reference to those who hold to the belief that cross 

 breeding, conjugation and amphimixis — the three terms 

 differ merely in degree — increase variability, it may be 

 well to inquire concerning some of the evidence which has 

 been instrumental in formulating the opinion. Without 



^Science, p. 907, 1908. 

 ^Science, p. 93 5, 1912. 



