1893. HYBRIDITY IN PLANTS. 205 
pollination of South African plants by birds. The Cinnyridz, or sun- 
birds, are exceedingly good pollinators, especially Nectarinia chalybea 
and bicollavis, and Promerops caper. Like bees, they, as a rule, visit 
only one species of flower ata 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 Cimnyris, is an 
important element in this pollination. Mr. H. N. Ridley calls 
attention to a remarkable structure in the flowers of Bulbophyllum 
macranthum and other orchids of Singapore for cross-pollination 
by the agency cf 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 Leguminose growing on the Omberg, an 
isolated mountainous region in Germany, chiefly covered with pine 
woods, ali 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 Pronuba 
yuccasella. 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 partially 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; 
