Cytology of a new variety of Ac hly a americana . 151 
microtome, double stained with gentian-violet and eosin, and 
mounted in xylol-balsam. 
An attempt was made to secure uniformity of treatment 
throughout, so that the differences observed in the nuclei 
might be safely referred to inherent causes and not to the 
varying nature of the method of preparation. A very large 
number of successfully stained preparations were examined, 
just as a systematist selects his type-plant after the examina- 
tion of thousands of individuals, so in the main are the figures 
which illustrate the cytology of this plant, while drawn as 
accurately as possible under the camera from actual examples, 
nevertheless typical, as they have been deliberately selected 
to represent what may be regarded as the normal type. 
An impression appears still to exist amongst some cyto- 
logists that sections, especially of such small objects as these 
oogonia and oospores are apt to be lost during the preparation 
of the slides, and that even if they are not, it is difficult and 
sometimes impossible to avoid mixing up the sections and so 
forming by a mental process a false picture of the object. 
Now, while diminution in size increases the difficulty of 
finding the series of sections which constitute the object, and 
involves an additional expenditure of time and patience, 
there should never be the least doubt in the mind of a com- 
petent observer as to whether his sections are really serial 
or not. If sections are loosened by accident, he should be 
in a position to put his finger, metaphorically speaking, on 
the vacant place. Even with such small objects as the 
oospores of Achlya any careful observer can be certain of 
the reality of his series even without recourse to the refine- 
ments of a mechanical stage and the measurement of the 
distance between the sections. 
In the preparations which I have made and used for further 
study, I have never seen a loose or misplaced section, and 
have never been at a loss to locate any section of a series. 
It is fortunate that it is possible to attain certainty in this 
direction, for there can be no doubt that the oogonia and 
oospores are too thick and dense for clear pictures of their 
