132 



GOOD FROM CROSSING. 



Chap. XVII. 



i V 



^■■_ 



t : f 

 •'J 1 



v j 





: 1f ! 



V, .V 



' V * * 

 ^ I 



w jp 



? 



w ■ 



close interbreeding. These facts are, however, connected with 

 our present subject, because a cross with a distinct individual 

 is shown to be either necessary or advantageous. Dimorphic 

 and trimorphic plants, though they are hermaphrodites, must 

 be reciprocally crossed, one set of forms by the other, in order 

 to be fully fertile, and in some cases to be fertile in any degree 

 But I should not have noticed these plants, had it not been 

 for the following cases given by Dr. Hildebrand : 59 



Primula sinensis is a reciprocally dimorphic species: Dr. Hildebrand 

 fertilised twenty-eight flowers of both forms, each by pollen of the other 

 form, and obtained the full number of capsules containing on an average 

 42*7 seed per capsule ; here we have complete and normal fertility. He 

 then fertilised forty-two flowers of both forms with pollen of the same 

 form, but taken from a distinct plant, and all produced capsules con- 

 taining on an average only 19'6 seed. Lastly, and here we come to our 

 more immediate point, he fertilised forty-eight flowers of both forms with 

 pollen of the same form, taken from the same flower, and now he obtained 

 only thirty-two capsules, and these contained on an average 18-6 seed, 

 or one less per capsule than in the former case. So that, with these 

 illegitimate unions,. the act of impregnation is less assured, and the fertility 

 slightly less, when the pollen and ovules belong to the same flower, than 

 when belonging to two distinct individuals of the same form. Dr. Hilde- 

 brand has recently made analogous experiments on the long-styled form 

 of Oxalis rosea, with the same result. 60 



It has 



ntly been discovered that 



pi 



growing in their native country under natural conditions, cannot 

 be fertilised with pollen from the same plant. They are some- 

 times so utterly self-impotent, that, though they can readily 

 be fertilised by the pollen of a distinct species or even distinct 

 genus, yet, wonderful as the fact is, they never produce a single 

 seed by their own pollen. In some cases, moreover, the plant's 

 own pollen and stigma mutually act on each other in a dele- 

 terious manner. Most of the facts to be given relate to Orchids, 



but I will commence with a plant belo 

 ferent family. 



lely dif- 



Sixty-three flowers of Corydalis cava, borne on distinct plants, were 

 fertilised by Dr. Hildebrand 61 with pollen from other plants of the same 

 species ; and fifty-eight capsules were obtained, including on an average 



59 'Botanische Zeitung/ Jan. 1864, 



s. 3. 



Berlin, 1866, s. 372. 

 61 International 



Hort, 



Congress 



i 



60 ' Monatsbericht Akad. Wissen,' London, 1866. 



