‘PARTHENOGENESIS IN THALICTRUM PURPURASCENS 373 
the two is evidenced by the change in the structure of the 
smic layer immediately in contact with the egg. Whether 
wnot the egg excretes an enzyme that digests the cytoplasm is 
matter of detail. The fact remains that physical changes are 
evident in the cytoplasm in contact with the egg, which then 
. Such changes may well vary the osmotic pressure 
the egg, and lead to nuclear division as shown by the 
“periments referred to above. 
While Thalictrum purpurascens is parthenogenetic under arti- 
‘cal conditions, parthenogenesis also takes place in plants grown 
t perfectly natural conditions if pollination be prevented, as 
wn by plants setting seed in the gardens when the flowers 
d with paper bags. All such plants showed quite a. 
any seeds per plant as those which had been fertilized and grew 
‘nthe field, Many flowers were cut from natural specimens in ae 
ompare them with the parthenogenetic material. In — 
= pollen tube could be detected, but in far the 
nber no such tube or any evidence of a tube ha 
could be seen. One can tell by even 2 
the micropyle whether a tube has been pres 
sg © conclude that many seeds are pro 
aie ity for pollination in order to p 
he plant is getting towards the habit of 
E en though ‘the number of recorde: 
4 among dicotyledons be so small, the. 
distributed. It would seem as if | 
much. more common occurrence am ng 
nt known. | : 
|) SUMMARY. > 
elopment and germination of th 
