56 



The Journal of Heredity 



yoked together, i)erjugatc llirough the 

 yoke. In conjugate hybrids we see the 

 results of jjrolonged partial conjuga- 

 tion, in per jugate hybrids the results of 

 previously completed conjugation. 



DIFFERENCES BETWEEN THE CLASSES. 



When the original germ-cells are so 

 different that conjugation cannot be 

 comjileted, no normal germ-cells are 

 formed by the conjugate generation, 

 and no perjugate generation follows. 

 The fact that it is often possible to 

 secure conjugates from hybrid combina- 

 tions that do not produce perjugates is 

 itself an evidence that the two genera- 

 tions re])rescnt different phenomena 

 of reproduction. The conjugate gen- 

 eration usualh' shows a general increase 

 of vegetative vigor over the parental 

 stocks, while perjugates are often weak 

 or defective. Another general difference 

 is that the individual members of a 

 conjugate generation are usually alike, 

 while the perjugates of the same stock 

 arc often very diverse. Thus when two 

 (hslinct types of cotton are crossed the 

 conjugate hybrids are as uniform as 

 the members of the parent stocks, or 

 even more uniform, but in the perjugate 

 generations a wide range of characters 

 may be shown, extending beyond the 

 parental types as well as between them. 

 The uniformity of the conjugates may 

 be ascribed to the fact that the nuclear 



elements derived from the parent germ- 

 cells are not fused or redistributed, but 

 are merely associated in the same cells, 

 much as different stocks may be united 

 by grafting. The diversity of the per- 

 jugates indicates that the nuclear ele- 

 ments have formed more intimate and 

 \-aried coml^inations.- 



In view of these essential differences 

 it is evident that the two classes of 

 hybrids must be formalh- recognized be- 

 fore any useful generalizations can be 

 framed. Of hybrids or of hybridization 

 as a whole, little or nothing can be said 

 that is not erroneous or misleading. All 

 of our general statements regarding the 

 nature, behavior or agricultural value 

 of hybrids relate to one of the two 

 classes, instead of to both. Conjugate 

 hybrids are of use chiefly in plants that 

 are adapted for vegetative propagation, 

 while seed-propagated varieties must be 

 secured by selection from perjugate 

 generations. Conjugate hybrids are 

 useful in some crops, perjugate hybrids 

 in others. In each experiment the 

 conjugates may be expected to show 

 one series of biological phenomena, 

 and the perjugates another, contrasting 

 series. For all scientific and i^ractical 

 purposes it is necessary to keep in 

 mind the differences between the two 

 classes of hybrids, and this would be 

 easier if distinctive names were em- 

 ployed . 



2 The nature and extent of the diversity that has been observed in cotton may be judged from 

 the photographs accompanying the more detailed paper on Perjugate Cotton Hybrids by Charles 

 G. Marshall. 



A Race Betterment Exhibit 



Desiring to render concrete .some of the i)()siti\-e suggestions matle at Battle 

 Creek in January, 1914, the Race Betterment Fund (which has recently recei\-ed 

 a permanent endowment of sS300,000) is arranging for a Race Betterment lixhibit 

 in the Educational Building of the Panama-Pacific Exposition at San Francisco. 

 The keystone of the exhibit will embody the constructive and practical methods 

 of race betterment, viz. : preventive medicine, social and j^ersonal h>-giene, child 

 and civic welfare agencies, ]:)racticable eugenic suggestions, etc., but a certain 

 amount of space will be devoted to the causes and evidences of race degeneracy. 

 The Eugenics Record Office will not have an exhibit as it had planni'd. 



