NOTES ON SOME CURIOSITIES OF ORCHID BREEDING. 483 



tion has not taken place. (Kerner and Oliver, " Nat. Hist. Plants," 

 ii. p. 415.) In my own observations in crossing distinct genera 

 of Orchids, Cattleya x Angraecum, Dendrobium x Epidendrum, 

 Dendrobium x Cattleya, Dendrobium x Odontoglossum, Epiden- 

 drum x Odontoglossum, in many cases the pollen tubes grew, 

 and the pods swelled slightly, but fertilisation did not take 

 place. 



In fully formed pods that have opened prematurely, and 

 have been found to be empty, nearly all have had bundles of 

 pollen tubes lying alongside the undeveloped ovules, sometimes 

 extending to the bottom of the pod, but with no traces of 

 fertilisation. 



Thus we see that the swelling of the pod and the growth of 

 the pollen tubes may be in a sense mechanical rather than 

 physiological, and therefore we should not attach too much 

 importance to the fact that the pod has developed to its normal 

 size after the application of foreign pollen. We should wait until 

 proper fertilisation has taken place and good seeds are produced 

 before venturing to think of success. Even then, if the seeds 

 germinate by proper treatment, and plants are raised, they may 

 refuse to flower, as in many Paphiopedium x Phragmipedium 

 crosses hitherto ; and if they flower they may not turn out to be 

 true hybrids as in the Zygopetalum crosses mentioned above. 

 " There's many a slip betwixt the cup and the lip." Never- 

 theless, whether we succeed or whether we fail, all these ex- 

 periments and observations are interesting, and add to our 

 knowledge of plant life. 



Fertility and Sterility of Hybrids. 



Before Darwin published his " Origin of Species " it was 

 generally held by naturalists that distinct species were seldom 

 fertile with one another, and that if hybrids were raised at all 

 they were quite sterile and barren ; and very often the whole 

 question was begged by classing those species that did cross as 

 varieties of one. Darwin made a most careful and elaborate 

 study of the whole question of hybridism, and came to the fol- 

 lowing conclusions : — " First crosses between forms sufficiently 

 distinct to be ranked as species, and their hybrids are very 

 generally, but not universally, sterile. . ; . The sterility is of 



