ARTHUR: PROBLEMS IN THE STUDY OF PLANT Rusts 3 
moistening with a drop of water. Moreover, dried specimens keep 
indefinitely in all their perfection of form and intimate structure, 
and also as a rule of color. Hence it has come about that the 
description of species and the general classification has been 
founded almost exclusively upon the spore forms. This was a 
necessity at first; but it is a crude and artificial method. It has 
led to no clearer understanding of the real relationships of the 
species than did the Linnaean system for flowering plants, with its 
countings of stamens and pistils. Yet this comparison does scant 
justice to the intricacies of the subject, and the difficulties under 
which the systematic uredinologist has labored. 
The student of phanerogamic plants, even back to the days of 
Linnaeus, has been well aware that few of the plants which come 
under his observation have more than one kind of flowers. The 
flower contains the pistils and stamens, from the interaction of 
which arises the fruit. Sometimes, to be sure, the pistils and sta- 
mens are in separate flowers on different parts of the plant, or even 
on different plants, as in the willows and poplars. But with rare 
exceptions, so rare as to have no appreciable effect upon the devel- 
opment of the subject, no material difficulty has been experienced 
in detecting the essential organs of reproduction, and no question 
has arisen regarding their association with the fruit which follows 
their appearance. 
In order to come to an appreciation of the conditions existing 
among the rusts, and some of the difficulties besetting systematists 
in trying to unravel relationships, let us suppose some changes in 
the phanerogamic world. Let us begin by supposing flowers to 
be wholly suppressed, so completely in fact that the fruit would 
appear to arise from swollen buds, as figs do in fact, only in the 
case we are supposing the flowers are so totally suppressed that 
even the microscope reveals no trace of them. Now in this 
imaginary world each kind of tree, shrub and herb may bear not 
only one form of fruit, but two, three, four or even five forms as 
different as peaches, acorns, chestnuts, beans and currants. Two 
or more of these may occur at the same time in any variety of 
combination. Often delicate, peach-like fruits will be produced in 
a succession of crops throughout the summer, then in the fall a 
crop of acorn-like fruits that are not injured by hanging on the 
