Chap. XVII. SELF-IMPOTENT PLANTS. 115 



fertilised above one hundred flowers of the above-mentioned Onci- 

 diurn flexuosum, which is there endemic, with its own pollen, and 

 with that taken from distinct plants : all the former were sterile, 

 whilst those fertilised by pollen from way other plant of the same 

 species were fertile. During the first three days there was no 

 difference in the action of the two kinds of pollen : that placed on 

 stigma of the same plant separated in the usual manner into grains, 

 and emitted tubes which penetrated the column, and the stigmatic 

 chamber shut itself ; but only those flowers which had been fertilised 

 by pollen taken from a distinct plant produced seed-capsules. On 

 a subsequent occasion these experiments were repeated on a large 

 scale with the same result. Fritz Muller found that four other 

 endemic species of Oncidiurn were in like manner utterly sterile 

 with their own pollen, but fertile with that from any other plant : 

 some of them likewise produced seed-capsules when impregnated 

 with pollen of widely distinct genera, such as Cyrtopodium, and 

 Eodriguezia. Oncidiurn crispum, however, differs from the fore- 

 going species in varying much m its self-sterility ; some plants 

 producing fine pods with their own pollen, others failing to do so 

 in two or three instances, Fritz Muller observed that the pods pro- 

 duced by pollen taken from a distinct flower on the same plant, were 

 larger than those produced by the flower's own pollen. In Eyidtn- 

 drum cinnabar inum, an orchid belonging to another division of the 

 family, fine pods were produced by the plant's own pollen, but they 

 contained by weight only about half as much seed as the capsules 

 which had been fertilised by pollen from a distinct plant, and in 

 one instance from a distinct species ; moreover, a very large propor- 

 tion, and in some cases nearly all the seeds produced by the plant's 

 own pollen, were destitute of an embryo. Some self-fertilised 

 capsules of a Maxillaria were in a similar state. 



Another observation made by Fritz Midler is highly remarkable, 

 namely, that with various orchids the plant's own pollen not only 

 fails to impregnate the flower, but acts on the stigma, and is acted 

 on, in an injurious or poisonous manner. This is shown by the 

 surface of the stigma in contact with the pollen, and by the pollen 

 itself, becoming in from three to five days dark brown, and then 

 decaying. The discoloration and decay are not caused by 

 parasitic cryptograms, which were observed by Fritz Muller in only 

 a single instance. These changes are well shown by placing on 

 the same stigma, at the same time, the plant's own pollen and 

 that from a distinct plant of the same species, or of another 

 species, or even of another and widely remote genus. Thus, 

 on the stigma of Oncidiurn flexuosum, the plant's own pollen and 

 that from a distinct plant were placed side by side, and in five days' 

 time the latter was perfectly fresh, whilst the plant's own pollen 

 was brown. On the other hand, when die pollen of a distinct plant 

 of the Oncidiurn fttxaosum and of the Epidendrum zebra (nw. 

 spec. ?) were placed together on the same stigma, they behaved in 

 exactly the same manner, the grains separating, emitting tubes, 



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