240 ILLEGITIMATE OFFSPRING OF CHAP. V. 



same heterostyled species, together with their illegiti- 

 mate offspring, resemble hybrid unions between distinct 

 species together with their hybrid offspring. In both 

 cases we meet with every degree of sterility, from very 

 slightly lessened fertility to absolute barrenness, when 

 not even a single seed-capsule is produced. In both 

 cases the facility of effecting the first union is much 

 influenced by the conditions to which the plants are 

 exposed.* Both with hybrids and illegitimate plants 

 the innate degree of sterility is highly variable in 

 plants raised from the same mother-plant. In both 

 cases the male organs are more plainly affected than 

 the female ; and we often find contabescent anthers 

 enclosing shrivelled and utterly powerless pollen- 

 grains. The more sterile hybrids, as Max Wichura 

 has well shown,t are sometimes much dwarfed in 

 stature, and have so weak a constitution that they are 

 liable to premature death ; and we have seen exactly 

 parallel cases with the illegitimate seedlings of Lythrum 

 and Primula. Many hybrids are the most persistent 

 and profuse flowerers, as are some illegitimate plants. 

 When a hybrid is crossed by either pure parent-form, 

 it is notoriously much more fertile than when crossed 

 inter se or by another hybrid ; so when an illegitimate 

 plant is fertilised by a legitimate plant, it is more 

 fertile than when fertilised inter se or by another ille- 

 gitimate plant. When two species are crossed and 

 they produce numerous seeds, we expect as a general 

 rule that their hybrid offspring will be moderately 

 fertile ; but if the parent species produce extremely 

 few seeds, we expect that the hybrids will be very 



* This has been remarked by chapter a striking illustration in 



many experimentalists in effecting the case of Primula veris. 

 crosses between distinct species ; t ' Die Bastnrdbefruchtung im 



and in regard to illegitimate Pflanzenreich,' 1865. 

 unions I have gi ven in the first 



