484 



SCIENCE 



[N. S. Vol. XXXIX. No. 1005 



tain data bearing on the results of close 

 breeding and cross breeding which differ 

 merely in degree from parthenogenesis 

 and amphimixis. The question is an im- 

 portant one, for if cross breeding is only- 

 valuable in sorting out and combining ex- 

 isting characters, it not only obscures the 

 facts, a knowledge of which is necessary 

 before progress can be made in building 

 up new characters, but results in no actual 

 advancement in cumulative evolution. 

 Here the material for study consisted of 

 scalariform or cross-bred and lateral or 

 close-bred (parthenogenetic) zygospores — 

 in reality the young individuals — of the 

 common filamentous green alga Spirogyra 

 inflata (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 zygo- 

 spores. The results were not in accord with 

 the general belief that cross breeding in- 

 creased variability, although studies by 

 Warren, Kellogg, Casteel and Phillips had 

 pointed out that this belief was not substan- 

 tiated 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 hypothesis pro- 

 posed on purely theoretical grounds by 

 Hatsehek 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 contin- 

 ually forming body cells becoming so varia- 

 ble through absence of control by amphi- 

 mixis, that eventually some one group of 

 functional importance fails to meet the 



i Science, p. 907, 1908; 



6 Science, p. 935, 1912. 



limits imposed by the environment. 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, inas- 

 much as the material was homogeneous in 

 every respect with the exception of the 

 manner of reproduction. 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 be- 

 lief 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 any de- 

 sire to be critical and at some risk of ex- 

 ceeding the controversial bounds which a 

 paper of this nature allows, a few of the 

 more important investigations touching 

 upon the subject will be considered. 



Castle, Carpenter, Clark, Mast and Bar- 

 rows (1906) in a series of observations as 

 to the effect of cross breeding and close 

 breeding on the variability and fertility of 

 the small fruit fly, Drosophila ampelophila 

 Loew., stated that "inbreeding did not af- 

 fect the variability in the number of teeth 

 on the sex comb of the male, nor the varia- 

 bility in size," basing the opinion on the 

 coefficient of variation in the number of 

 spines and the standard deviation in the 

 length of the tibia. In the former case the 

 data certainly do not permit a clear con- 

 clusion one way or the other, but the value 

 of the character which represents the sum 

 of the teeth of the sex combs of the right 



