Chap. V. HETEROSTYLBD TRIMORPHIC PLANTS. 211 



whilst others are fully fertile, or possibly fertile in 

 excess. 



The last point which need here be noticed is that, 

 as far as the means of comparison serve, some degree 

 of relationship generally exists between the infertility 

 of the illegitimate union of the several parent-forms 

 and that of their illegitimate offspring. Thus the 

 two illegitimate unions, from which the plants in 

 Classes VI. and VII. were derived, yielded a fair 

 amount of seed, and only a few of these plants are in 

 any degree sterile. On the other hand, the illegiti- 

 mate unions between plants of the same form always 

 yield very few seeds, and their seedlings are very 

 sterile. Long-styled parent-plants, when fertilised 

 with pollen from their own-form shortest stamens, ap- 

 pear to be rather more sterile than when fertilised with 

 their own-form mid-length stamens; and the seedlings 

 from the former union were much more sterile than 

 those from the latter union. In opposition to this re- 

 lationship, short-styled plants illegitimately fertilised 

 with pollen from the mid-length stamens of the long- 

 styled form (Class V.) are very sterile; whereas some 

 of the offspring raised from this union were far from 

 being highly sterile. It may be added that there is a 

 tolerably close parallelism in all the classes between 

 the degree of sterility of the plants and their dwarfed 

 stature. As previously stated, an illegitimate plant 

 fertilised with pollen from a legitimate plant has its 

 fertility slightly increased. The importance of the sev- 

 eral foregoing conclusions will be apparent at the close 

 of this chapter, when the illegitimate unions between 

 the forms of the same species and their illegitimate off- 

 spring, are compared with the hybrid unions of dis- 

 tinct species and their hybrid offspring. 



