stout: pollinations in cichorium intybus 443 



stamens. A third form may here arise with stamens and pistils of 

 nearly equal length and intermediate between the lengths in the 

 other two forms (see diagram by Scott '65, p. 109). Here also 

 all plants are evidently more or less self-fertile, the plants of the 

 non-dimorphic form being highly self-fertile. There is also marked 

 fertility of intra-form crosses. The inter-form crosses are, how- 

 ever, more fertile; a condition that very clearly arises from the 

 fact that the relative morphological and physiological differentia- 

 tion of the sex organs involved is such that the greater degree of 

 similarity exists between the male and female organs borne by 

 plants of different forms. 



Still another degree of morphological differentiation in herma- 

 phrodites with perfect flowers is seen in Lythrum Salicaria (see 

 diagram by Darwin, '65, p. 171). in which three forms differ in 

 regard to length of styles and in the particular combination of 

 three different types of stamens. The forms are all different in 

 respect to pistils but each is like another form in respect to one 

 set of stamens. A special point of interest is the differentiation 

 in the male sex organs in a single flower, which are relatively 

 morphologically differentiated quite as are the two sets in various 

 species of Labiatae and Cruciferae. Here, however, there are 

 various physiological or functional differentiations, giving various 

 grades of ^ compatibility. All plants are apparently strongly 

 self-sterile; there is marked sterility in intra-form cross-pollina- 

 tions (all illegitimate); there is also marked sterility in inter- 

 form pollinations, involving stamens and pistils of different 

 lengths (illegitimate), but high fertility if legitimate pollinations 

 are made. In inter-form crosses any one plant is both sterile and 

 fertile to another plant according to the pollen used. We have 

 here, perhaps, the most convincing evidence that in one mdi- 

 vidual the male sex organs may exhibit further differentiation, 

 giving two sets of stamens in which the stamen as a whole, and 

 each set as a whole, are differentiated quite independently of any 

 differentiation that may exist between the spores produced by a 



stamen. 



The degrees of functional differentiations that exist in such 

 plants as those above mentioned are conspicuous because they 

 exist in more or less marked correlation with structural differ- 

 entiations. They are, however, revealed only in the degree of 

 fertility and sterility that results. 



