131 



at the same time, as for example, of a half dozen varieties of apples^ 

 corn, etc.; or the same kind of pollen may be treated to different 

 strengths of the sugar solution, all other conditions remaining the 

 same. For example, the poUinia of four native Asclepiads were 

 tested in this manner. The poUiaia were placed in pure water, 

 ^0%, 25%, 50%, 75% and full strength. The tubes developed 

 from the outer angle of the pollinium in all these cases, but with 

 water the growth was small in both number and length of tubes. 



■ 



The same was true of the full strength and the best results were 



and 75% solutions, the percentage uidi- 

 cating that with Asclepias verticillata, for example, the most 

 favorable strength is 65%. 



As another illustration, the white variety of Tjadescantia 

 Virginica has 15% of abortive pollen and the normal form only 



The perfect pollen of both sorts germinate with equal 

 rapidity, frequently tubes of \oo p in length being produced in 

 two hours. 



These wells are adapted for ttie study of the two kinds of 

 pollen in dimorphic plants. As far as experiments have gone in 

 this direction the indications are that the larger pollen, designed 

 for the long styles, germinate quicker and the tubes grow more 

 rapidly than with the smaller grains. 



Some kinds of pollen seem to be quite indifferent to the 

 strength of the solution. Others are extremely sensitive and only 

 respond when all conditions are most favorable. A decided low- 

 ering of the temperature is quite sure to check the activity of 

 pollen. Many tests will terminate negatively during a cold sum- 

 mer rain. As far as observed, light— the heat remaining con- 

 stant—has no influence. It has been a common practice to set 

 pollen for germination at nightfall and get a supply of tubes the 

 next morninsf. 



Only a little work has been done In growing pollen upon for- 

 eign stigmas, but enough to Indicate that many kinds of grains 

 are not inactive upon the stigmas of other than the same species. 

 The lily family affords good subjects for this study, as the stigmas 

 are frequently large and adhesive. Erythronmm albidum, for 

 example, when in the center of a boquet of other flowers, may 

 furnish stlemas bearine several sorts of germinating i)ollcn. 



fc,""" "v-^i'-to 



Rutgers Colle-e. BVRON D. Halsted. 



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