place, the vacuoles diminish in size. This 

 phase is not reversible. In other cases the 

 protoplasm of the cell is broken down by auto- 

 matic processes, as a result of which all that 

 remains are a few fat globules. 



In order to determine the changes in viscosity 

 of protoplasm under X irradiation, Breslavets 

 (1936) selected pollen grains as objects in which 

 these changes can be most easily observed by 

 means of centrifugation since the greater part of 

 these individual cells, at a certain stage in their 

 development, becomes filled with a large num- 

 ber of starch granules, which can be displaced 

 by centrifugation. In this respect the pollen 

 grains of hyacinth are particularly convenient, 

 since the transparent integument of the grains 

 permits microscopic observation of the entire 

 thickness of the protoplasm. Preliminary experi- 

 ments have shown that, depending on the time of 

 irradiation, a greater or lesser displacement 

 of the starch granules takes place. The follow- 

 ing method was used for the determination of the 

 viscosity of the protoplasm: the centrifuge tubes 

 were filled with 5 cubic centimeters of 10% 

 solution of cane sugar; into each of the four tubes 

 one anther from the same flower was placed, 

 and the centrifuge set in motion (2000 rpm). 

 After 5 minutes, an anther was removed from 

 one of the tubes and placed on a microscope 

 slide with a drop of iodine in potassium iodide, 

 and the centrifuge was set in motion once more. 

 After 15 minutes a second anther was removed 

 and placed on a cover glass, a third was re- 

 moved after 30 minutes, and a fourth after 60 

 minutes. Due to the action of the iodine the 

 starch granules became dark blue in color and 

 their displacement (which depended on the dura- 

 tion of centrifugation) within the pollen grain 

 could be easily observed. A 5 -minute action 

 [of the centrifuge] cleared 1/6 of the space from 

 starch granules; 15 minutes, 1/2; 30 minutes, 

 2/3; and 60 minutes, 3/4. Thus, the displace- 

 ment of starch granules is proportional to the 



time of action of the centrifugal force. Prelimi- 

 nary experiments have shown that the viscosity 

 of protoplasm in young pollen grains is very 

 great. It is precisely these young pollen grains 

 which had to be used for the experiment, since 

 in them the starch granules reach their maxi- 

 mum size. For this reason, experiments to 

 study protoplasmic viscosity were begun with 

 large doses of X rays. The conditions of irra- 

 diation were as follows: 220 kilovolts, 5 mil- 

 liamperes, distance from the tube: 70 millime- 

 ters, no filters (Table 24). 



These experiments indicate that the viscosity 

 of the protoplasm begins to increase only with 

 the action of 4000 r, and that it continues to 

 increase up to a dose of 48, 000 r, inclusive. 

 Apparently, the centrifugation method is too 

 coarse to distinguish finer differences in vis- 

 cosity of the protoplasm due to X irradiation. 

 It is interesting to note that pollen grains germi- 

 nated even after the action of such doses as 

 48,000 r. Microscopic examinations (Bresla- 

 vets, 1937) indicate that only doses of 16, 000 r 

 begin to change the structure of protoplasm, 

 making it more coarsely grained. 



Erdmann (1936) investigated the relationship 

 between the loss of water contained in proto- 

 plasm and the action of X rays. The author 

 points out that yeast is an object in which it is 

 possible to measure the water content in living 

 cells, and that it is possible in yeast to measure 

 the effect of X rays by the depression of their 

 ability to multiply. The water content was 

 measured by: 1) hypertonic solution, 2) drying 

 in a desiccator, 3) natural aging of the yeast 

 cells. 



It should be kept in mind that all plant cells 

 contain free water in addition to water bound in 

 the protoplasm. By removing this water with 

 hypertonic solutions it is possible to cause a 

 shrinking of protoplasm [due to loss of water]. 



Table 24 



The effect of centrifugal force on the displacement of starch granules 



in irradiated pollen after various time intervals. 



(based on Breslavets' data, 1936b) 



61 



