ARTHUR: IMPORTANCE OF THE SPERMOGONIUM 115 
ning of the nuclear cycle. During germination the one nucleus 
divides into four, one for each of the four sporidia. By the time 
the sporidium is ready to form mycelium, its nucleus has sep- 
arated into two, lying side by side, and henceforth these paired 
nuclei maintain an independent existence. When a new cell of 
the mycelium or a conidiospore is formed, each of the paired 
nuclei divides, half of each remaining in the old cell and half 
going to the new one. Thus the two associated nuclei have an 
independent line of descent from the time of leaving the sporidium 
of the germinating teleutospore until they arrive in a teleutospore 
again. 
This account of nuclear phenomena has been given to show 
that the life-cycle of a rust begins with the germinating teleuto- 
spore, that is, the sporidium; that the spermogonium is a prob- 
lematical organ quite saz generis; and that all other sorts of rust 
spores are of a conidial or asexual character. 
The spore-forms of the rusts and the spore-bearing structures 
present an endless diversity, which is one of the charms of the 
study, and at the same time is a source of perplexing difficulties. 
There are, however, but two types of uredineal conidia; the 
aecidium and the uredo. These have received different names 
when presenting different aspects, and it may be well to mention 
the more common of these appellations. When the aecidial 
peridium is elongated and dehisces by numerous longitudinal slits 
the aecidium is called a roestelia, a form found on pomaceous 
hosts ; when the peridium is extended and breaks irregularly we 
have a peridermium, which occurs on coniferous hosts ; when the 
peridium is wanting the aecidium is called a cacoma. The uredo, 
when it assumes a resting state, has spores with indurated, brown 
walls and persistent pedicels, which are called amphispores. But 
throughout all the variety of forms, the aecidiospore and the ured- 
Ospore retain their conidial character. 
It is not always easy to decide whether a certain spore-struc- 
ture is an aecidium or a uredo, and it would not be difficult to 
point out many instances where they are confused in the — 
Writings of some of the most eminent uredinologists, were it not 
both ungracious and uncalled for to do so. In general they may 
be distinguished by the spores of the aecidium always being pro- 
