288 REPRODUCTION 



Orchidacese, Iridacese and Scrophulariacese : on the other hand, 

 among the Cruciferae, Leguminosse and Umbelliferse hybrids are 

 uncommon. 



True hybrids or crosses between distinct species of plants 

 usually exhibit the following characters : — 



(i) If the parents are very widely different from each other, 

 the offspring is usually delicate and difficult to rear, but where 

 the parents are more nearly related the offspring is frequently 

 taller and more vigorous and luxuriant in its vegetative organs 

 than either of the parents. 



(ii) In nearly all cases hybrids are less fertile than their 

 parents : their sexual organs are weak, and frequently they are 

 absolutely sterile, the anthers producing no pollen or the carpels 

 no ovules, so that seed-formation is impossible. In certain rare 

 instances there appears no inclination or power to form flowers. 

 In those which do produce flowers and seeds the pollen-grains 

 are generally smaller in size and number, and the ovules more 

 or less imperfectly formed : the male reproductive organs are more 

 deleteriously affected than the female organs. 



(iii) The petals and coloured parts of the flower are generally 

 larger and more lasting than those of either parent. ' Doubling ' 

 of the flowers and other pathological malformations are more 

 common among hybrids. 



(iv) In the first generation raised from seeds obtained by 

 cross-pollinating distinct species, all the individual plants are, in 

 most instances, similar to each other, and resemble both parents : 

 their characters in regard to form and size of root, stem, leaf 

 and flower are intermediate between the two. 



The individuals of the second or later generations, that is, 

 the offspring which arise from self-pollination or cross-pollination 

 of the flowers of hybrids, vary much in form and in other ways : 

 they do not resemble each other nearly so much as those of 

 the first generation. Some of them almost exactly resemble 

 the female, others the male parent, while many show the 



