134 Scientific Proceedings (ioo). 



somes characteristic of the species, (b) the proportion of mixed 

 dams of each possible pure chromosome-number used in each 

 generation, (c) the relative fecundity of dams of different pure 

 chromosome-number, and (d) the number of generations through 

 which the system is carried. 



3. By the pure-sire method, without selection in the F 5 gen- 

 eration in a twelve-chromosome (haploid) species (including man), 

 the probability that a given offspring carries absolutely no mongrel 

 blood, i. e., mongrel-descended chromosomes is 1:0.205. 



4. For mass improvement without selection the pure-sire method 

 in a twelve-chromosome (haploid) species, ceases to be practically 

 effective after the F 5 generation. 



75 (i45o) 



The transformation of the plant ovule into an ovary. 



By J. Arthur Harris. 



[From the Station for Experimental Evolution, Carnegie Institution 

 of Washington, Cold Spring Harbor, N. Y.] 



In plants there is a rather wide capacity for the development 

 of organs of various kinds from primordia normally destined to 

 produce quite different structures. For example, leaves may 

 replace petals, stamens or carpels; petals may occur in the place 

 of stamens or carpels. The transformation of stamens into 

 carpels is a well-known phenomenon. 



Furthermore, the continued development of a growing point 

 the activity of which is usually terminated by the formation of 

 some highly specialized organ, such as the flower or fruit, is quite 

 familiar to those concerned with problems of variation. 



Among these morphological abnormalities the continued 

 meristematic activity of the axis which is normally terminated by 

 the formation of the ovary is of very rare occurrence. It is, how- 

 ever, regularly found, although in a small and variable percentage 

 of the cases, in one of the passion flowers, Passiflora gracilis. 

 Here prolification of the fruit consists in the formation of series 

 of carpels, which may or may not be ovuliferous, within the 



