190 MR. C. DARWIN ON THE SEXUAL RELATIONS OF 
of stamens, borne by the two other forms, of corresponding lengths, 
comes out conspieuously. In the mid-styled form the distended 
pollen-grains from the longer stamens had nearly double the 
diameter of those from the shorter stamens; so that there is a 
greater difference in this respect than in Z. salicaria. In the 
long-styled form, also, the difference in diameter between the 
pollen-grains of the longer and shorter stamens was plainer than 
in L. salicaria. These comparisons, however, must be received 
with caution, as they were made on specimens long kept in a 
dried condition. 
Lythrum thymifolia.—This form, according to Vaucher*, is 
dimorphie like Primula, and therefore presents only two forms. 
I received two dried flowers from Kew, which presented two 
forms: in the one form the stigma projected far beyond the calyx, 
in the other it was included within the calyx; in this latter form 
the style was only one-fourth of the length of the style of the 
other form. There are only six stamens; these are somewhat 
graduated in length, and in the short-styled form the anthers 
stand a little above the stigma, but yet the stamens by no means 
equal in length the pistil of the long-styled form; in the long- 
styled form the stamens are rather shorter than in the other 
form. These six stamens alternate with the petals, and corre- 
spond homologically with the longer stamens of L. salicaria and 
L. Grefferi. As there are only six stamens, it is scarcely possible 
that this species can be trimorphic. 
Lythrum hyssopifolia.—This species is said by Vaucher, but I 
believe erroneously, to be dimorphic. I have examined dried 
flowers from twenty-two separate plants from various localities, 
kindly sent to me by Mr. Hewett C. Watson, Prof. Babington, and 
others. These were all essentially alike. Hence the species cannot 
be dimorphic. The pistil varies somewhat in length, but when un- 
usually long the stamens are likewise generally long ; in the bud the 
stamens are short: perhaps these circumstances deceived Vaucher. 
There are from six to nine stamens, graduated in length; the sta- 
mens which are variable in being present or absent correspond with 
the six shorter stamens of L. salicaria and with the six which are 
absent in L. thymifolia. The stigma is included within the calyx, 
and stands in the midst of the anthers, and would generally be 
fertilized by them; but as the stigma and anthers are upturned, 
and as, according to Vaucher, there is a passage left in the upper 
side of the flower to the nectary, there can hardly be a doubt that 
* Hist. Phys. des Plantes d'Europe, tom, ii. (1841) pp. 869, 371. 
