4 ARTHUR: PROBLEMS IN THE STUDY OF PLANT RusTS 
plants all winter. But more curious than this, the seeds from one 
kind of fruit rarely produce a plant that will bear the same kind 
of fruit again. If the acorn-like seeds are planted, the plants that 
are grown may bear acorns, but are rather more likely to bear 
fruits enclosed in sacs like chestnuts. To some extent this alter- 
nation of forms appears to be haphazard, at least dependent upon 
conditions not understood, but to a large extent it seems to be a 
question of the species. If acorn-like fruits from one species of plant 
are sown they give rise to plants bearing currants, soon followed 
on the same plants by chestnuts. When the chestnuts from this 
species are sown the resulting plants bear peaches, followed on the 
same individual plants by acorns. But there is no predicting what 
combinations will occur in any one species. When different kinds 
of fruits are found on the same individual they are known, of 
course, to belong to the same species, but when on separate plants 
their connection can only be told by actual planting. To further 
complicate matters one kind of fruit, the currant we will suppose, 
has seeds that cannot be made to develop into a plant, although 
they will germinate ; and their purpose in the economy of the — 
cannot be conjectured. 
Let us fancy now that all plants of this imaginary world are 
exceedingly small, even the largest trees not being half the size 
of a pin, while the smaller plants are mere specks, in fact micro- 
scopic. How long do you think it would take botanists, with a 
flora of this sort, to become acquainted with the different varieties 
of each kind of fruit, and to connect the several forms into the 
cycle of true species ? 
In this fanciful sketch I have tried to portray some of the 
simplest conditions that exist among the rusts, using the fruits of 
currants, chestnuts, peaches, acorns and beans to represent respec- 
tively spermogonia, aecidia, uredo, teleutospores, and amphispores,. 
in order to show how complicated they are in comparison to the 
conditions that exist among flowering plants. If I have succeeded 
in making my analogy clear, it can be readily understood that the 
earlier botanists gave names to each spore-form, believing it to 
represent the whole species. Thus Uredo segetum was the name 
of the red rust of wheat, Puccinia graminis the black rust of wheat, 
Aecidium Berberidis the cluster-cup rust of barberry bushes ; and 
