i862.] ON PLANTS OF THE SAME SPECIES.' 48! 



Of all the German authors (but they are not many) whose 

 works I have read, you write by far the clearest style, but 

 whether this is a compliment to a German writer I do not 

 know. 



[The two following letters refer to the small bud-like 

 " Cleistogamic " flowers found in the violet and many other 

 plants. They do not open and are necessarily self-fertilised :] 



C. Darwin to J. D. Hooker. 



Down, May 30 [1862]. 



.... What will become of my book on Variatio ? I am 

 involved in a multiplicity of experiments. I have been 

 amusing myself by looking at the small flowers of Viola. 

 If Oliver* has had time to study them, he will have seen the 

 curious case (as it seems to me) which I have just made 

 clearly out, viz. that in these flowers, the few pollen grains 

 are never shed, or never leave the anther-cells, but emit long 

 pollen tubes, which penetrate the stigma. To-day I got the 

 anther with the included pollen grain (now empty) at one 

 end, and a bundle of tubes penetrating the stigmatic tissue 

 at the other end ; I got the whole under a microscope with- 

 out breaking the tubes ; I wonder whether the stigma pours 

 some fluid into the anther so as to excite the included grains. 

 It is a rather odd case of correlation, that in the double sweet 

 violet the little flowers are double ; i. e. y have a multitude of 

 minute scales representing the petals. What queer little flow- 

 ers they are. 



Have you had time to read poor dear Henslow's life ? 

 it has interested me for the man's sake, and, what I did 

 not think possible, has even exalted his character in my 

 estimation 



* Shortly afterwards he wrote : " Oliver, the omniscient, has sent me a 

 paper in the ' Bot. Zeitung,' with most accurate description of all that I 

 saw in Viola." 

 45 



