442 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



I, 2, 3, — X. The appearance within a species of one or more 

 groups of indi\'iduals which are respectively similarily 

 differentiated with regard to certain types, grades, or 

 combinations of differentiation as indicated in I and II. 



The existence and interrelations of \'arious types of these differ- 

 entiations with reference to the questions of sterility may be 

 illustrated by those cases in which inconii^atibilities giving sterility 

 are best known. 



In Linum grandiflonim (Darwin, '64) there is such anatomical 

 differentiation that two groups (usually spoken of as forms) of 

 individuals exist in respect to the type of pistil present in the 

 perfect flowers. The flowers of all individuals of one form have 

 long styles and short stamens; those of the other form have short 

 styles arjd short stamens. Aside from this evident morphological 

 differentiation there is a correlated functional differentiation. All 

 plants show marked self -sterility, according to the e\idence; thus 

 within the individual there is a degree of functional differentiation 

 of the sex organs that gives self-incompatibility. It can not be 

 too strongly emphasized that this is not correlated closely with 

 anatomical differentiation, for long-styled plants are fertile with 

 pollen from short stamens of plants of the other form, but sterile to 

 its own short stamens. Also a short-styled plant is fertile with 

 pollen of short stamens of a long-styled plant, but sterile with 

 pollen of its own short stamens. This is quite identical with the 

 behavior of cross-fertility and cross-sterility in Cichorium with 

 the exception that in Cichorium the differentiation is purely 

 physiological. 



Darwin reports comj)lete intra-form incompatibility in Linum; 

 plants of the same form are cross-sterile; the two sex organs of 

 different plants of the same form show the same incompatibilities 

 exhibited by the two sex organs of the single plant. The morpho- 

 logical differences are certainly not indicative of the incom- 

 patibilities. Many highly self-fertile species show greater rela- 

 tive morphological differences than are here seen even in the long- 

 styled form. 



In several species of Primula (Darwin '62; Scott '65) there is a 

 further anatomical differentiation between the two forms in that 

 they differ in the relative length of both sex organs: one form has 

 long styles and shtjrt stamens, the otluT h:i-> short styles and long 



