Chap. XVII. 



SELF-IMPOTENT PLANTS. 



133 



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 had been possible, for the anthers not only touch the 

 stigma, but the pollen-tubes were seen by Dr. Hildebrand to penetrate it ; 

 nevertheless these eighty-four flowers did not produce a single seed- 

 capsule ! This whole case is highly instructive, as it shows how widely 

 different the action of the same pollen is, according as it is placed on the 

 stigma of the same flower, or on that of another flower on the same raceme, 

 or on that of a distinct plant. 



With exotic Orchids several analogous cases have been observed, chiefly 

 by Mr. John Scott. 62 Oncidium sphacelatum has effective pollen, for with 

 it Mr. Scott fertilised two distinct species ; its ovules are likewise capable 

 of impregnation, for they were readily fertilised by the pollen of 0. divari- 

 cation; nevertheless, between one and two hundred flowers fertilised by 

 their own pollen did not produce a single capsule, though the stigmas 

 were penetrated by the pollen-tubes. Mr. Kobinson Munro, of the Eoyal 

 Eotanic Gardens of Edinburgh, also informs me (1864) that a hundred 

 and twenty flowers of this same species were fertilised by him with 

 their own pollen, and did not produce a capsule, but eight flowers ferti- 

 lised by the pollen of 0. divaricatum produced four fine capsules : again, 

 between two and three hundred flowers of 0. divaricatum, fertilised by 

 their own pollen, did not set a capsule, but twelve flowers fertilised by 0. 

 flexuosum produced eight fine capsules : so that here we have three utterly 

 self-impotent species, with their male and female organs perfect, as shown by 

 their mutual fertilisation. In these cases fertilisation was effected only 

 by the aid of a distinct species. But, as we shall presently see, distinct 

 plants, raised from seed, of Oncidium flexuosum, and probably of the other 

 species, would have been perfectly capable of fertilising each other, for this 

 is the natural process. Again, Mr. Scott found that the pollen of a plant 

 of 0. microchilum was good, for with it he fertilised two distinct species ; 

 he found its ovules good, for they could be fertilised by the pollen of one 

 of these species, and by the pollen of a distinct plant of 0. microchilum ; 

 but they could not be fertilised by pollen of the same plant, though the 

 pollen-tubes penetrated the stigma. An analogous case has been recorded 

 by M. Eiviere, 63 with two plants of 0. Cavendishianum, which were both self- 

 sterile, but reciprocally fertilised each other. All these cases refer to the 

 genus Oncidium, but Mr. Scott found that Maxillaria atro-rubens was 

 " totally insusceptible of fertilisation with its own pollen," but fertilised, 

 and was fertilised by, a widely distinct species, viz. M. squalens. 



As these orchids had grown under unnatural conditions, in hot- 



62 'Proc. Bot. Soc. of Edinburgh,' 

 May, 1863 : these observations are given 

 in abstract, and others are added, in the 

 ' Journal of Proc. of Linn. Soc.,' vol. viii. 



Bot., 1864, p. 162. 



63 Prof. Lecoq, ' De la Fecondation,' 

 2nd edit., 1862, p. 76. 



