786 H. E. Knowuton 
dependent on the kind and intensity of the adverse condition. While 
these changes are going on, it is naturally difficult to judge whether or 
not the protoplasm is viable. 
DISCUSSION OF RESULTS 
The results of the studies with the pollen of Antirrhinum majus (snap- 
dragon) and of Zea Mays (corn) show the striking dissimilarities between 
them. In the pollen of Antirrhinum, metabolic activity is weaker than 
in the corn pollen, as evidenced by less respiration, lower water content, 
and greater ability to withstand extremes in temperature. It would seem 
that the factors influencing longevity of Antirrhinum pollen are the same 
as in certain kinds of seeds. Desiccation, exhaustion of stored foods, 
and decrease of essential enzymes do not appear to be important. These 
same factors have not been found to be important in the loss of vitality 
of the seeds. Altho the author has no data to substantiate this, the 
theory of Crocker and Groves (1915) that death is caused’ by slow precipi- 
tation of proteins within the protoplasm, seems to be the most logical. 
The increase in reducing sugars, with increasing age, is evidence in favor 
of this theory, for it shows that some readjustment is taking place. 
When corn pollen is subjected to normal atmospheric conditions, 
drying out undoubtedly determines the duration of vitality. When 
stored under conditions of high humidity, however, the vitality is not 
greatly prolonged. Altho respiratory activity is great, no marked loss 
of reserve materials occurs. As with Antirrhinum pollen, some destructive 
change must be going on within the protoplast. A change in the proto- 
plasmic emulsion, such as precipitation, would affect the imbibitory 
powers of the colloids and might cause the excretion of water noted in 
the experiments. 
With pollen, one must distinguish two degrees of vitality, one which 
ean bring about germination and short tube growth, and another which 
will cause fertilization to take place. The author has given considerable 
evidence in these experiments that a pollen grain may germinate without 
ever functioning in fertilization. It is an open question whether this 
is due merely to the inability of the pollen tube to reach the ovary. Polli- 
nation experiments, under favorable temperatures, on short styles or 
styles of which the major parts have been severed, with a study of 
tube growth within the style, would shed some light on this. 
