404 BOTANY [CHAP. XI 



Letter 727 strongly suspect that they serve as reservoirs for water. 1 But 

 1 shall experimcntise on this head. A thin slice is a beautiful 

 object, and looks like coarsely reticulated glass. 



If you have an old plant which could be turned out of its 

 pot (and can spare the time), it would be a great gain to me 

 if you would tear off a bit of the roots near the bottom, and 

 shake them well in water, and see whether they bear these 

 minute glass-like bladders. I should also much like to know 

 whether old plants bear the solid bladder-like bodies near the 

 upper surface of the pot. These bodies are evidently enlarge- 

 ments of the roots or rhizomes. You must forgive this long 

 letter, and make allowance for my delight at finding this new 

 sub-group of insect-catchers. Sir E. Tennent speaks of an 

 aquatic species of Utricularia in Ceylon, which has bladders 

 on its roots, and rises annually to the surface, as he says, by 

 this means. 2 



We shall be delighted to see you here on the 26th ; if you 

 will let us know your train we will send to meet you. You 

 will have to work like a slave while you are here. 



Letter 728 To J. Jenner Weir. 



In 1870 Mr. Jenner Weir wrote to Darwin: "My brother has but 

 two kinds of laburnum, viz., Cytisus purpureus^ very erect, and Cytisus 

 alpinus, very pendulous. He has several stocks of the latter grafted 

 with the purple one ; and this year, the grafts being two years old, I saw 

 in one, fairly above the stock, about four inches, a raceme of purely 

 yellow flowers with the usual dark markings, and above them a bunch 

 of purely purple flowers ; the branches of the graft in no way showed an 

 intermediate character, but had the usual rigid growth of purpureus" 



Early in July 1875, when Darwin was correcting a new edition of 

 Variation under Domestication, he again corresponded with Mr. Weir 

 on the subject. 



Down, July 8th [1875]. 



I thank you cordially. The case interests me in a higher 

 degree than anything which I have heard for a very long 

 time. Is it your brother Harrison W., whom I know? I 

 should like to hear where the garden is. There is one other 

 very important point which I am most anxious to hear viz., 



1 The existence of water-stores is quite in accordance with the 

 epiphytic habit of the plant. 



3 Utricularia stellaris. Emerson Tennent's Ceylon, Vol. I., p. 124, 

 1859. 



