No. 587] SHORTER ARTICLES AND DISCUSSION 705 



the fruits are twice as long. The capsules sometimes reach the 

 length of 70 mm. and average above 60 mm. ; they are very much 

 the longest fruits reported in the subgenus Onagra. Bartlett re- 

 gards this large size of capsule as the origin of a new character. 

 Now capsule size obviously depends upon the number of ovules 

 produced which develop into seeds. It thus becomes an impor- 

 tant matter to obtain the data on ovule sterility in the species 

 Reynolds!! and the derived forms stmlalta, debilis and bilonga. 

 Ovule sterility is widespread among the Oenotheras as all stu- 

 dents of the genus know. Should it be found that bilonga pro- 

 duces a very much greater number of ovules than debilis and the 

 other types this fact would indicate a true progressive advance. 

 It may, however, be found that the smaller size of the capsules of 

 llajnoldsii si inialla. and di hills is due to ovule sterility, i. e., to 

 the inability of a large proportion of the ovules to set seed. This 

 would point to a very different interpretation of the conditions in 

 bilonga, and might indicate that bilonga is an example of rever- 

 sion towards an ancestral type in which a large capsule was corre- 

 lated with a high degree of ovule fertility. 



In the comments which I have presented on the extremely 

 interesting facts discovered by Bartlett no attempts have been 

 made to offer exact explanations in line with Mendelian analysis. 

 It is not difficult to spin hypotheses on assumptions which have 

 been neither established nor disproved, but such creations are 

 hardly worth the effort when the facts are within grasp. My 

 main point is a constant questioning of the genetic purity of the 

 material with which Bartlett has worked from the standpoint 

 developed in my forthcoming paper £ ' The Test of a Pure Species 

 of Oenothera."* It is impossible to discuss this subject in the 

 short space of a review. The most important test is that of cross- 

 breeding with the purest species known, to judge from the uni- 

 formity of the P, hybrid generation whether or not the parent 

 types are pure. I also firmly believe that all exact genetical work 

 on Oenotheras must make use of methods of experimental germi- 

 nation to ensure complete progenies from the viable seeds and tc 

 permit the preservation of a residue of ungerminated structures 

 that may be examined. 5 There is in addition the determination 



* To appear in the Proceedings of the American Philosophical Society, 

 Vol. LIV, 1915. 



5 Davis, B. M., "A Method of Obtaining Complete Germination of Seeds 

 in (Enothera and of Recording the Residue of Sterile Seed-like Structures," 

 Proc. Nat. Acad. Sci., Vol. I, p. 360, 1915. 



