i893. HYBRIDITY IN PLANTS. 205 



pollination of South African plants by birds. The Cinnyridae, or sun- 

 birds, are exceedingly good pollinators, especially Nectarinia chalybea 

 and bicollaris, and Pyomevops caper. Like bees, they, as a rule, visit 

 only one species of flower at a time. Mr. Scott Elliot believes that 

 the identity of colour — an unusual shade of red — in the majority of 

 ornithophilous flowers and on the breast of species of Cinnyris, is an 

 important element in this pollination. Mr. H, N. Ridley calls 

 attention to a remarkable structure in the flowers of Bulbophyllum 

 macmnthum and other orchids of Singapore for cross-pollination 

 by the agency of insects. C. Correns describes the special 

 arrangements for this purpose in Salvia and Calceolaria. Lists of 

 cross-pollinated plants are given by McLeod from Belgium and 

 the Pyrenees, by E. Loew and Knuth from Germany, by Delpino, 

 from Italy, and by Scott Elliot from Madagascar. Kellgren 

 enumerates 33 species of Leguminosae growing on the Omberg, an 

 isolated mountainous region in Germany, chiefly covered with pine 

 woods, all pollinated by lepidoptera. The mode of pollination in the 

 different species of Yucca is of great interest, and has long attracted 

 the attention of botanists. Professor Riley, who has made it a 

 subject of special study, states that in all the species examined by 

 him, self-pollination is almost impossible ; and that in each species 

 the pollination is effected by a single species of insect. The 

 pollinator of Yucca filamentosa is a moth, the female of Pronuha 

 yiiccasella. The object of the visit of the moth is the deposition of its 

 eggs in the ovules of the Yucca, the coats of which it pierces. This 

 is always effected as soon as the flower opens ; and the moment an 

 egg has been deposited the insect rushes to the anthers and carries a 

 quantity of pollen to the stigma, stuffing it into the stigmatic cavity 

 with its proboscis. Ten or twelve ovules may thus be destroyed, 

 but the number in each ovary is so large that this does not practically 

 affect its fertility. In Philadelphia, where the moth makes its 

 appearance about the time that the Yucca is in flower, the latter 

 produces abundance of seed, while it does not set its fruit in 

 Washington and St. Louis, where it flowers a fortnight before the 

 arrival of the moth. Finally, the report, in the Botanical Gazette, of a 

 series of experiments carried on by Miss M. Reed, mostly on petunias, 

 fully confirms Darwin's statement that cross-pollinated produce 

 more seed-vessels than self-pollinated plants, and that the capsules 

 are heavier. 



Attention has long been called to the fact that not a very small 

 number of plants produce, in addition to their ordinary showy 

 flowers, others — termed cleistogamic — which never open, in which 

 the corolla is partiall}' or entirely suppressed, but which ripen 

 abundance of seeds, being, of course, self-pollinated. A very good 

 example of these cleistogamic flowers is furnished by the various 

 species of "dog" violet, Viola sylvatica and its allies. The con- 

 spicuous flowers which appear in the early spring are mostly sterile ; 



