368 THE AMERICAN MONTHLY [Dec 



hawthorn, houeysuckle, Scotch fir, mountain ash, ane- 

 mone, buttercup, nettle, primrose, violet, willow-herb, 

 bedstraw, dock, and many other plants are all different 

 and belong to distinct species. Seen v/ith the lens the 

 cluster-cups present the appearance of a group of mina- 

 ture volcanoes. At first the a-cidium fruit is a small 

 spherical body formed beneath the epidermis of the leaf 

 whereon it grows, which it ultimately ruptures; the fecid- 

 ium itself, when ripe, bursts, and the yellow spores are 

 discharged. The section of an aecidium shows a cup-like 

 cavity with spores arranged in vertical rows like 

 short strings of beads; they are developed by budding, and 

 become detached in succession. Externally the aecidium 

 is in most species invested by a membranous envelope, 

 the peridium, usually cup-shaped, but occasionally, as in 

 the cluster-cups of the pine, prolonged into a tube. The 

 peridium may open irregularly or split up in a definite 

 manner, giving its margin a toothed appearance. An 

 aecidiospore can germinate wlien sown on a suitable 

 host. The cluster-cups appear earlier in the season than 

 the uredo- or telutospores, and are very often associated 

 with smaller caps called spermogonia, which appear on 

 the upper surface of the leaf (fig. 5, a spm.), from which 

 issue minute spermatia, which have never been known to 

 germinate, and are therefore generally regarded as male 

 reproductive cells. 



All the three kinds of spores above described, it must 

 now be explained, are produced in succession by some of 

 the Uredines on the same mycelium. The Puccinias of 

 the mint, primrose, violet, goat's-beard, and onion de- 

 velop all three forms ; teluto- uredo- and aecidiospores 

 occur on the same })laut. Had we examined the bramble 

 Phragmidium earlier in the season we should have found, 

 not the many-celled telutospores, but unicellular uredo- 

 or aecidiospores. The rose rust. Ph. subcorticimi, and 

 that of the barren strawberry, Fh. fragariae, in like 



