JET. 61.] TO CHARLES DARWIN. 631 



River, through its finest scenery up to St. Paul, Min- 

 nesota ; saw the falls of St. Anthony and Minne- 

 haha ; thence, while the rest of our party essayed Lake 

 Superior, Mrs. Gray and I returned home by rapid 

 stages. 



I have only to-day finished the study and laying 

 into the herbarium of specimens I gathered and dried, 

 regretting the while that I did not collect more speci- 

 mens and many other species, as I might have done. 



Tyndall is in Boston, and I trust will be with us 

 next week. I have not yet seen him, nor Fronde, nor 

 even MacDonald, the third lecturing notability in 

 Boston. 



TO CHARLES DARWIN. 



CAMBRIDGE, October 6, 1872. 



You delight me by your promise to take up Dio- 

 na3a and Drosera now, and I imagine you as now 

 about it. Good ! And I am so glad you will take 

 that opportunity to collect your botanical and quasi- 

 botanical papers. These, with the Dionsea, etc., will 

 make a nice and most welcome volume. 



In answer to your query, I think I can " support 

 the idea," or the probability of it, "that tendrils 

 become spiral after clasping an object from the stimu- 

 lus from contact running down them." For though 

 some "tendrils do become spiral when they have 

 clasped nothing," others do not. The adjustment of 

 the unstable equilibrium is more delicate in the 

 former, so that it starts under some inappreciable 

 cause or stimulus. That the stimulus may be so pro- 

 pagated downward is clear in the sensitive plant, 

 where the closing of the leaflets in succession will fol- 

 low the closing of the ultimate pair under slight and 



