Chap. XVII. EVIL FROM INTERBREEDING. 113 



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

 for the following cases given by Dr. Hildebrand : 66 — 



Primula sinensis is a reciprocally dimorphic species: Dr. Hilde- 

 brand 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 containing on an average only l',r6 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 and 

 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. Hildebrand has recently made analogous experiments on the 

 long-styled form of OxaJis rosea, with the same result. 67 



It has recently been discovered that certain plants, whilst 

 growing in their native country under natural conditions, 

 cannot be fertilised with pollen from the same plant. They 

 are sometimes 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 is the fact, 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 deleterious manner. Most of the facts to be 

 given relate to orchids, but I will commence with a plant 

 belonging to a widely different family. 



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

 were fertilised by Dr. Hildebrand 68 with pollen from other plants of 

 the same species; and fifty-eight capsules were obtained, including 

 on an average 4'5 seed in each. He then fertilised sixteen flowers 

 produced by the same raceme, one with another, but obtained only 

 three capsules, one of which alone contained any good seeds, 

 namely, two in number. Lastly, he fertilised twenty-seven flowers, 

 each with its own pollen; he left also fifty-seven flowers to be 

 spontaneously fertilised, and this would certainly have ensued if it 



68 ' Botanische Zeitung,' Jan. 1864, Berlin, 1866, s. 372. 

 s - •'• 68 International Hurt. Congress, 



8? ' Monatsbericht Akad. Wissen,' London, 1866. 



VOL. II. 



