5 18 MISCELLANEOUS BOTANICAL LETTERS. [1881. 



present wish to learn something of the causes of variation. 

 He imagined to himself wonderful galls caused to appear on 

 the ovaries of plants, and by these means he thought it pos- 

 sible that the seed might be influenced, and thus new varieties 

 arise. He made a considerable number of experiments by 

 injecting various reagents into the tissues of leaves, and with 

 some slight indications of success.] 



Aggregation. 



[The following letter gives an idea of the subject of the 

 last of his published papers.* The appearances which he 

 observed in leaves and roots attracted him, on account of 

 their relation to the phenomena of aggregation which had so 

 deeply interested him when he was at work on Drosera :] 



C. Darwin to S. H. Vines, f 



Down, November I, 1881. 

 My dear Mr. Vines, — As I know how busy you are, it 

 is a great shame to trouble you. But you are so rich in 

 chemical knowledge about plants, and I am so poor, that I 

 appeal to your charity as a pauper. My question is — Do you 

 know of any solid substance in the cells of plants which 

 glycerine and water dissolves ? But you will understand my 

 perplexity better if I give you the facts : I mentioned to you 

 that if a plant of Euphorbia peplus is gently dug up and the 

 roots placed for a short time in a weak solution (1 to 10,000 

 of water, suffices in 24 hours) of carbonate of ammonia the 

 (generally) alternate longitudinal rows of cells in every root- 

 let, from the root-cap up to the very top of the root (but not 

 as far as I have yet seen in the green stem) become filled 

 with translucent, brownish grains of matter. These rounded 

 grains often cohere and even become confluent. Pure phos- 

 phate and nitrate of ammonia produce (though more slowly) 

 the same effect, as does pure carbonate of soda. 



* 'Journal of the Linnean Society.' Vol. xix., 1882, pp. 239 and 262. 

 f Reader in Botany in the University of Cambridge. 



