Chap. V. HETEROSTYLED TRIMORPHIC PLANTS. 189 



short-styled form; so that the long-styled can be fer- 

 tilised legitimately in two ways and illegitimately in 

 four ways. The same holds good with respect to the 

 mid-styled and short-styled forms. Therefore with 

 trimorphic species six of the eighteen unions yield 



legitimate offspring, and twelve yield illegitimate off- 

 spring. 



I will give the results of my experiments in detail, 

 partly because the observations are extremely trouble- 

 some, and will not probably soon be repeated — thus, I 

 was compelled to count under the microscope above 

 20,000 seeds of Lythrum salicaria — but chiefly because 

 light is thus indirectly thrown on the important sub- 

 ject of hybridism. 



Lythrum salicaria. 



Of the twelve illegitimate unions two were com- 

 pletely barren, so that no seeds were obtained, and of 

 course no seedlings could be raised. Seedlings were, 

 however, raised from seven of the ten remaining 

 illegitimate unions. Such illegitimate seedlings when 

 in flower were generally allowed to be freely and 

 legitimately fertilised, through the agency of bees, by 

 other illegitimate plants belonging to the two other 

 forms growing close by. This is the fairest plan, and 

 was usually followed; but in several cases (which 

 will always be stated) illegitimate plants were fer- 

 tilised with pollen taken from legitimate plants be- 

 longing to the other two forms; and this, as might 

 have been expected, increased their fertility. Lythrum 

 salicaria is much affected in its fertility by the nature 

 of the season; and to avoid error from this source 

 as far as possible, my observations were continued 

 during several years. * Some few experiments were 



