314 
M. R. ENSIGN 
above was employed in treating thick, leathery leaves. For thin, succulent 
ones, like grape leaves, the following modifications were necessary to insure 
success : 
1 . The nitric acid must be diluted to about 50 percent. 
2. The length of time necessary for clearing is shorter. 
3. The stain should be diluted to 0.5 percent. 
4. Complete penetration of the stain is effected in about 12 hours. 
In other respects the procedure is the same as that given for the heavier 
leaves. 
Examination of Material and Determinations. All the determinations 
of vein-islets were made by projecting the magnified image of the stained 
vascular system by the use of a micro-projection apparatus. This consists 
of a horizontally placed microscope through which a stream of light, derived 
from an electric arc, is permitted to pass. The section to be studied was 
placed upon the stage of the microscope. The light is absorbed by the 
stained bundles and they appear as a shadow upon white paper. The paper 
was always placed at the same distance from the ocular of the microscope 
in making determinations. Adjustment was made so that a piece of paper 
75 mm. square would just take a projected image from 4 sq. mm. of leaf 
surface. Now by marking with a lead pencil in the center of each of the 
vein-islets, the number of islets in 4 sq. mm. of leaf surface was quickly 
and accurately determined. The average area of each islet, then, was 
computed by dividing 4 sq. mm. by the number of vein-islets in that area. 
Percentage of Seeds Producing Polyembryonic Seedlings 
Webber (1900) states that the majority of Citrus seeds produce poly- 
embryonic seedlings. Aside from this statement no data are available 
on this point. Therefore some germination tests were conducted as follows: 
tin basins were filled nearly full of sawdust which had been previously 
washed and sterilized. Upon this a layer of cheesecloth was laid and the 
seeds were placed upon the cheesecloth. Then another layer of cloth and 
more sawdust were added. The seeds prior to planting were treated for 
six hours in a 7 percent solution of calcium hypochlorite. These precautions 
eliminated a good many of the contaminating fungi. 
It was found that seeds subject to desiccation in storage for only ten 
days had lost their vitality. Therefore all the seeds for this test were taken 
from the grapefruit and planted immediately. Germination began after 
a period of five days and continued for fourteen days. 
Table i is a summary of these tests. 
The results show that a high percentage of the fresh seeds are viable. 
Despite the precautions taken against contamination, the majority of the 
seeds which did not germinate were infected. This was indicated by the 
fact that these seeds rotted, and also by the fact that a higher percentage 
of germination was obtained when the seeds germinated in pure culture. 
