302 The American Naturalist. [April, 



cell in the body of the ovule. How in the inverted ovule 

 they grow downward and then turn and retrace their steps 

 upward; and the same question mighl properly be asked 

 in regard to the lower plants. How does the antherozooid of 

 Fucus succeed in finding the oosphere which is floating, per- 

 haps, at some distance in the water, or the antherozooid of a 

 moss plant, the small mouth of the archegonium which is on 

 a different plant. As to this we can only suggest. It has 

 boon thought that in such cases the ovum secretes some 

 substance which acts as a chemical excitant on the anthero- 

 zooids. Pfeffer working from this suggestion, has surely ob- 

 served some interesting phenomena, that much strengthen if 

 not absolutely confirm this hypothesis. His method of exper- 

 imenting was this : — A solution of the substance to be experi- 

 mented upon was placed in capillary tubes of from 5-7 hun- 

 dredths of a millimeter wide. These capillary tubes dip into 

 a watch crystal containing liquid wherein (juantities of the 

 antherozoids have been placed. Currants of diffusion will, it 



that in the watch, crystal, and when the substance experi- 

 mented upon is the right one the antherozooids are seen to fol- 

 low the currents of diffusion and enter the capillary tube. In 

 ferns Pfeffer found malic acid or malate to be the effective sub- 

 stance attracting the antherozooids. As a proof of this, malic 

 acid is found in abundance in prothallium decoctions of ferns 

 and is known to be of very common occurrence throughout the 

 vegetable kingdom. In the moss plant, cane sugar was found 

 to be the effective substance and substances of the closest 

 analogy as glucose, levulose, glycogen, etc., were found to exer- 

 cise no attraction. Thus Pfeffer formulated an antherozooid 



test for these substances, analogous to the ba 



eteria test for oxy- 



.gen invented by Englemann. 





In the growth of the pollen tube from the 



stig.na downward 



to the embryo sac, a conducting tissue is for 



tried which accom- 



plishes the same purpose. The conducting 



tiesue consists of 



layers of specialized cells which become til 



led with nutritive 



saccharine material and furnishes nourish: 



ment to the pollen 



tube in its downward growth. Frequently 



we find continuous 



