
a“ 
OVULE ‘ANDEMBRYO OF POTAMOGETON NATANS. 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY. 
G. M. HOLFERTY. 
(WITH PLATES II AND III AND ONE FIGURE) 
THIs investigation was begun several years ago, and was 
continued as time permitted. Material from a number of stations 
in the vicinity of Chicago was collected, and other collections 
have been added. From this material about seven hundred 
slides of microtome sections have been prepared and studied. 
The work was done under the direction of Professor John M. 
Coulter and Dr. Charles J. Chamberlain. 
— 
MATERIAL AND METHODS. 
The collections were made in June, July, and August. Those 
made in June show some young spikes still within the cone- 
shaped spathe, while others are just issuing from it. Early in July 
the flowers open and pollination is effected, while in August the 
seed comes to maturity. 
The spikes were cut off with a sharp scalpel and dropped at 
once into the 1 per cent. solution of chrom-acetic acid. After 
remaining in the solution from 36 to 48 hours, the material was 
washed in warm water, and then allowed to remain in running 
tap water 20 to 24 hours. After imbedding in paraffin the 
material was cut on a Minot microtome, the sections being from 
6~—13m in thickness. 
Combination stains were used for all work, cyanin and 
my throsin proving most satisfactory, particularly for sporogenous 
.Ussues. The safranin gentian-violet orange G combination gave 
very satisfactory results for chromosomes and all phases of 
mitosis. The length of time sections should be left in each 
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