i865 1881] F. MULLER 365 



nearly in the zenith ; but I doubt whether this parahelio- Letter 687 

 tropism will be observable in England. To-day, though con- 

 tinuing to be fully exposed to the sun, at 3 p.m. the leaves 

 had already returned to a nearly horizontal position. As soon 

 as there are ripe seeds I will send you some ; of our other 

 species of Pkyllanthus I enclose a few seeds in this letter. 



In several species of Hedychium the lateral halves of the 

 leaves when exposed to bright sunshine, bend downwards so 

 that the lateral margins meet. It is curious that a hybrid 

 Hedychium in my garden shows scarcely any trace of this 

 paraheliotropism, while both the parent species are very 

 paraheliotropic. 



Might not the inequality of the cotyledons of Citrus and 

 of Pachira be attributed to the pressure, which the several 

 embryos enclosed in the same seed exert upon each other ? 

 I do not know Pachira aqitatica, but [in] a species, of which I 

 have a tree in my garden, all the seeds are polyembryonic, 

 and so were almost all the seeds of Citrus which I examined. 

 With Coffea arabica also seeds including two embryos are 

 not very rare ; but I have not yet observed whether in this 

 case the cotyledons be inequal. 



I repeated to-day Duval-Jouve's measurements * on Bryo- 

 phyllum calycinum ; but mine did not agree with his ; they 

 are as follows : 



Distances between the tips of the upper pair of leaves. 



January gth, 1881 3 A.M. i P.M. 6 P.M. 



First plant . . 54 mm. . . 43 mm. . . 36 mm. 



2nd 28 25 23 



3rd . 28 . 27 27 



4th 51 46 39 i 



5th 61 52 45 



222 193 I7O 



To F. M tiller. Letter 688 



Down, Feb. 23rd, 1881. 



Your letter has interested me greatly, as have so many 

 during many past years. I thought that you would not 



1 Power of Movement in Plants^ p. 237. F. Miiller's measurements 

 show, however, that there is a tendency in the leaves to be more highly 

 inclined at night than. in the middle of the day, and so far they agree 

 with Duval-Jouve's results. 



