1892.] Botany. 777 
biosis. The beauty and perfectness of adaptation is, however, yet 
more marked than I have outlined. Prof. Riley observes that Yuccas 
are very irregular in flowering, that a plant which flowers this year 
may not next year. This irregularity might prove fatal to Pronuba, 
but a beautiful device is found to meet it. Yueca moths are equally 
irregular, a large percentage of the moths failing to issue the year fol- 
lowing oviposition, but are retarded until the second, third or fourth 
years after oviposition. 
What is the meaning of the phenomena here observed? We are 
dealing, it is seen, with a case of pollination widely different from other 
known cases. In the most highly specialized protandrous flowers as 
in Impatiens, pollination by an insect or humming bird is entirely 
accidental. In the protogynous flowers of Aristolochia and Arum, so 
much admired for their beautiful device for securing cross pollifation, 
carrying the pollen is an entirely unintentional action on the part of 
the gnats and flies, they going merely where they are allured. In the 
most perfect device of the many beautiful ones in orchids, the pollinia 
merely: accidentally adhere to the insect and are carried from flower 
to flower as he flies about in search of nectar. Indeed, of all the 
beautiful and ingenious devices by which cross pollination is accom- 
plished by animate beings, so far as known, Yugea is the only case 
where this apparently intelligent pollination occurs. In all other cases 
it is accidental. 
Similar cases of apparently intelligent action among insects fre- 
quently occur, where food is provided beforehand for the larve. Such 
illustrations are the collecting of honey, the storing up of insects 
and spiders which have been killed for the purpose, or the laying of 
eggs in a branch or fruit stem which is afterwards girdled to provide 
dried material for the larval development. Between all of these 
devices, however, and Yucca pollination, there is, it appears to me, a 
wide difference. Such devices are the inherited resultants of easily 
understood facts or laws. The difference is merely a difference of 
degree truly. Such a difference as exists between the trained botanist 
and the rude understanding of the native American. The latter 
would understand that a girdled limb would in all probability die. 
Such things even his dull intellect will notice, as illustrations occur 
every day before his eyes. He could hardly be made to understand, 
however, that there is such a thing as sex in plants, although illustra- 
tions demonstrating this occur just as commonly under his eye. The 
nature of the problem is different. I do not credit the Yucca moth 
with a full understanding of what she is doing but it does seem that 
