to the Plant Cell . 
539 
VI. Summary. 
1. The algae studied thrive best in artificial cultures which remain 
neutral or slightly acid in reaction. The phanerogams studied thrive 
better in a solution which remains neutral or slightly alkaline in 
reaction. 
2 . Potassium salts were found necessary for the germination and growth 
of certain mosses. When a certain sub-minimal amount of potassium was 
present, there was some evidence that certain moss spores could germi- 
nate and avail themselves of sodium during the embryonic stages of 
development. 
3. In all green plants studied, potassium was essential for starch 
formation. 
4. Mitotic cell division did not take place without a suitable supply 
of potassium, although a certain amount of growth by stretching was 
possible. The transfer of stimulated cells from one potassium-free solution 
to another potassium-free solution of slightly different composition enabled 
a few cells to divide. 
5. The lack of phosphorus seemed to be more injurious to the cells 
studied than the lack of any other element. 
6. Cells in a state of phosphorus starvation first lose the soluble 
phosphorus complexes; later the injury extends to the strictly living organs 
of the cell, finally resulting in its death. 
7. Phosphorus appears to be more closely connected with carbohydrate 
transformation than with the origin of those substances. In the absence of 
phosphorus abnormal transformations occurred. 
8. In the absence of phosphorus no mitotic divisions were possible. 
Cells which had lived for some time in the absence of phosphorus were 
difficult to stimulate to divide. 
9. Calcium appears to be necessary for the activity and growth of the 
chlorophyll and chlorophyll-containing organs. 
10. One of the most important functions of calcium seems to be the 
antidoting power it possesses for overcoming the bad effects of magnesium. 
There is evidence that the same function may be performed in part by 
sodium. 
11. Antheridia were produced in large numbers on Gymnogramme 
prothalli cultivated in solutions lacking calcium, but archegonia were 
not found. 
12. Cell nuclei were able to divide mitotically in the absence of calcium 
salts, but new cell-walls were imperfectly formed, if at all. The inability to 
form cellulose was also exhibited by the zygotes of Spirogyra. 
13. Spore formation in Aspevgilhis niger was more abundant when 
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