150 Trow . — Observations on the Biology and 
has described in the case of Achlya americana , without 
indicating, however, any reason for the anomaly. 
Such observations as these could be extended greatly by 
any one who devoted himself specially to the work, and it is 
possible that in this direction a solution of the real difference 
between the asexual reproduction by sporangia and sexual 
reproduction by apogamous oogonia may be found. 
Cytological observations on Serial Sections. 
Methods. Before proceeding to indicate the results of the 
study of the cytology of this plant, it will perhaps be advisable 
to indicate the methods adopted by me in securing well- 
stained preparations in the form of serial sections. The fixing 
liquid used was a saturated aqueous solution of mercuric 
chloride, and it was applied hot as advised by Hartog and 
Humphrey. Differences in the preparations led me to 
investigate the effect of differences in the temperatures. 
Accordingly specimens were fixed in a solution of mercuric 
chloride maintained for twenty to thirty minutes at 55 0 C., 
65° C., 75 0 C., 85° C. and 95 0 C. The differences in the results 
were not very great and it is possible that they were due in 
part to slight differences in the cultures. The solutions did 
not act uniformly on all the organs ; as might be expected, 
the conditions for fixing young oogonia and ripe oospores 
cannot be exactly alike. The temperature of 55 0 C., however, 
appeared to give uniformly good results, and all of the figures 
are from material prepared at this temperature or that of 
65° c . 
The material was dehydrated by means of graded alcohols — 
3°%, 5°°/o> 7°°/o’ 9°°/o anc ^ absolute — the transference from 
one to the other being made very slowly, drop by drop, and 
occupying, as has been said, the greater part of a week. The 
passage of the dehydrated material into paraffin was carried 
out in a similar manner, through the medium of xylol or 
chloroform, occupying the greater part of another week. 
The sections were cut of uniform thickness by a Jung- 
