344 BOTANY [Chap. XI 



Letter 669 if so he would deserve a Royal medal. I know it is not new ; 

 but how wonderful his account of the spermatozoa of some 

 dioecious alga or conferva, swimming and finding the minute 

 micropyle in a distinct plant, and forcing its way in ! Why, 

 these zoospores must possess some sort of organ of sense to 

 guide their locomotive powers to the small micropyle ; and 

 does not this necessarily imply something like a nervous 

 system, in the same way as complemental male cirripedes 

 have organs of sense and locomotion, and nothing else but 

 a sack of spermatozoa ? 



Letter 670 To F. Hildebrand. 



May 1 6th, 1866. 



Since writing to you before, I have read your admirable 

 memoir on Salvia} and it has interested me almost as much 

 as when I first investigated the structure of orchids. Your 

 paper illustrates several points in my Origin of Species \ espe- 

 cially the transition of organs. Knowing only two or three 

 species in the genus, I had often marvelled how one cell of the 

 anther could have been transformed into the moveable plate 

 or spoon ; and how well you show the gradations. But I am 

 surprised that you did not more strongly insist on this point. 



I shall be still more surprised if you do not ultimately 

 come to the same belief with me, as shown by so many 

 beautiful contrivances, — that all plants require, from some 

 unknown cause, to be occasionally fertilised by pollen from 

 a distinct individual. 



II. — Correspondence with Fritz Muller, 



1865— 1 881. 



The letters from Darwin to Muller are given as a separate group, 

 instead of in chronological sequence with the other botanical letters, as 

 better illustrating the uninterrupted friendship and scientific comradeship 

 of the two naturalists. A short biographical note on Fritz Muller is given 

 in Vol. I., p. 382. 



Letter 671 To F. Muller. 



Down, Oct. 17th [1865]. 



I received about a fortnight ago your second letter on 

 climbing plants, dated August 31st. It has greatly in- 

 terested me, and it corrects and fills up a great hiatus in 

 1 Pringsheim's Jahrbiicher, Vol. IV., 1866. 



