272 FRANCIS DAKWIN, 



absorption. Dr. Gilbert (p. 5) gives the amount of ammonia which 

 falls in rain and minor aqueous deposits per acreatRothamsted as 

 6*46 pounds per annum. Boussingault^ found '00079 grm. per 

 litre of ammonia in rain water in the country districts of France. 

 In dew he found as much as from '001 to "006 grm. per litre. 

 The average of three analyses here given of the amount of 

 organic matter in rain water is '028 grm. per litre. Is it not 

 possible that some of this organic matter (which causes rain 

 water to putrify when kept) may be absorbed by the filaments ? 

 On the whole, it does not seem impossible that a plant should 

 derive benefit from the nitrogen in the rain and dew which falls 

 on its leaves. 



Conchisions. 



The following is a summary of the results which I believe to 

 be established on a reasonable basis of probability : 



1. That the filaments are not parasitic organisms, but are 

 the normal productions of a particular form of glandular tri- 

 chomes on the leaves of the seedling and second-year ])lants. 



2. That they consist of protoplasm in some way intimately 

 connected with resinous matter. 



3. That the function of the protoplasmic portion of the 

 filament was originally to assist in the act of secretion, but that 

 it has been subsequently utilised by the plant as a mode of 

 nutrition. 



4. That the protoplasmic filaments have the power of absorb- 

 ing nitrogenous matter, and that in the seedlings they probably 

 absorb ammonia from the rain-water and dew. In the adult 

 plants they absord the products of the decaying insects for the 

 capture of which the plant is adapted. 



5. That some obscure correspondence may exist between the 

 protrusion of the filaments and the process of aggregation. 



Note to Mr. Francis Darwin's Paper. 



I beg leave to say that I have witnessed almost all the facts 

 described in the foregoing paper, and can vouch for their accu- 

 racy. To the best of my judgment, the whole case is a most 

 remarkable one, and well deserves the attention of physiologists. 



Charles Darwin. 



1 ' Watts' Diet, of Chemistry,' v, p. lOli-15. 



