240 The Pedigree Families. 



forms the slightest trace of pollen.^ With the pollen of 

 i^amarckiana or any of its deviations it is perfectly fertile 

 and gives a proportion of /a/a-plants which varies about 

 15-20%. 



Julius Pohl has investigated the cause of its steril- 

 ity.^ The pollen sacks of the open flower are dry to the 

 touch ; they seem to be empty, but as a matter of fact 

 contain a little pollen which is seen under the microscope 

 to consist of empty grains which are not merely poor in 

 protoplasm but shrivelled and stunted. The development 

 of the anthers is at first normal, up to the formation of 

 tetrads. About this time the surrounding cells of the 

 tapetum elongate ; and subsequently grow into the cav- 

 ity of the sack. These cells disappear at a later stage, 

 when the pollen grains may be found lying in the mucus 

 which they leave behind. 



I spent a great deal of time in transferring these 

 scanty masses of pollen to the stigma in the hope of 

 obtaining a few seeds if possible, but all in vain. If 

 the visits of insects were prevented the plants set no seed. 



The exclusively female character of this mutant is 

 very important, for it shows in a most direct way that 

 the remarkably regular production of O. lata year after 

 year in the Lamarckiana-i3.m\\y cannot be due to acci- 

 dental crossing — an explanation of the frequency and 

 regularit}^ of its appearance which is also disproved by 



' Of late I have discovered a hybrid strain of lata which produces 

 pollen in a greater or smaller part of its flowers. These plants, when 

 self-fertilized, produce seed, which gives 15-20 % examples of lata] 

 and 80-85 ^c of Lamarckiana. Also the same figures as by pollina- 

 tion with the parent-species. This proves the O. lata to be an in- 

 constant species. Seeds of this strain have been distributed to some 

 of my correspondents, who also found the type to be inconstant. — 

 (Note of 1908.) 



"Julius Pohl, Ucher Varintionszvcite dcr Oenothera Lamarc- 

 kiana, Oesterr. bot. Zeitschrift, 1895, Nos. 5-6. 



