i 9 o8] GATES— REDUCTION IN OENOTHERA 19 



POLLEN DEGENERATION 



The general question of pollen degeneration in Oenothera is an 

 interesting one. It reaches its extreme expression in O. lata, which 

 is usually completely sterile in this regard, and in which I have 

 already shown (11) that irregularities occur during the reduction 

 divisions similar to those found in sterile hybrids. The question of 

 sterility is evidently, as Tischler (32) suggests, a relative one. 



In O. rubrinervis one is led from a gross examination to judge 

 that the pollen production is copious and probably equal to that of 

 O. Lamarckiana itself, but in reality many of the pollen mother cells 

 fail to complete their divisions. From an examination of sections of 

 anthers of O. rubrinervis it is found that in some loculi a large number 

 or perhaps nearly all the mother cells may be degenerating in the 

 synapsis stage. Frequently the cells are flattened and distorted, 

 appearing pressed together for lack of space in the loculus. The 

 chromatic contents of such cells often form a dense irregular mass, or 

 their nuclei may be in normal synapsis or mitosis, notwithstanding the 

 distorted shape of the cell; while still other cells of the same loculus 

 may be entirely normal. Even earlier, in the archesporial stage, the 

 tapetal cells in many sections were found to be breaking down, as in 

 O. lata (11). No indications of degeneration have yet been observed 

 in mother cells of O. Lamarckiana, and very few in the tapetum. 



The percentage of mother cells which thus degenerate in O. 

 rubrinervis was not determined. Tischler (32) suggests that the 

 causes of sterility' in mutants are the same as those in hybrids and in 

 plants under cultivation. This general cause he designates as a 

 disturbance or derangement of the constitution of the idioplasm, which 

 he thinks has taken place in the production of mutants as well as in 

 hybrids and under the conditions of cultivation. 



PROTOPLASMIC CONNECTIONS 



It is an interesting fact that large and rather conspicuous proto- 

 plasmic connections are found between the pollen mother cells in 

 O. rubrinervis. They are usually quite easily seen and it is probable 

 that they are always present. They consist of delicate strings or 

 threads of cytoplasm connecting adjacent mother cells. In size they 

 vary greatly, from the delicacy of a spindle fiber to a coarse thread or 



