(57) 



permitted, I should have been glad to submit this plant to the inspection of 

 others before, perhaps, thus exposing my own incapacity. The only similar 

 figure which I have seen is in Schleiden's Principles of Scientific Botany, 

 London, 1849. Plate '2, Fig. 8. This cannot be the plant. 



Of the four recorded United States species of Ci/sfopns, three were 

 found. These are exceedingly common on the plants indicated. They do 

 not, however, have the blighting eifect of the Peronosporioe. Plants thor- 

 oughly dotted with their pustules appeared to survive without great injury. 

 Their microscopic character is so well known to botanists that nothing 

 would have been gained by selecting new specimens to figure, so in my haste 

 copies were selected as indicated. The other figures are from the collec- 

 tion, but none of the plants are more common than these. 



Cystopus candidus, Lev.^ {Plate I, Figs. 1, 2, 3^ 4.) Common on cru- 

 ciferous plants, notably here on horse radish and cabbage. 



C. cubicus, Mart. On Ambrosia artemisiscfolia , i\iQ common xdig weed. 



C. bliti, Bivon. On Portv.laca oleracea (purslane) and Amaranthus 

 retrojiexus. 



Perisporiacei. Notwithstanding the similarity of the names of these 

 families, the plants are very diff'erent, as a glance at the plates will show. 

 They, however, agree in their injuries to living plants, constituting very 

 many of the leaf blights of this and other countries. Some of them are 

 most exquisitely beautiful under the magnifier, a thing which the disciples 

 of the development theory of species have not yet accounted for. Their 

 beauty surely does not come from natural or sexual selection. The myce- 

 lium runs over the surface of the leaves, never appearing to enter the cel- 

 lular structure, yet, in some way, deriving nourishment from it. Here 

 applications, as of sulphur, have direct eff'ect. Here, too, the vine and the 

 hop mildews belong. Conidia are borne in moniliform strings arising from 

 the mycelium. The two together often give the aflected leaves a dusty, 

 whitened appearance, as if coated with whitewash. Later the spherical 

 bodies — conceptades^oi dark color, as represented in the plates, are 

 formed, sometimes exceedingly numerous, sometimes few and hard to find. 

 The conceptacles have not yet been discovered in the vine disease of Europe. 

 These conceptacles have at length radiating oppendafies, difi'erent from the 

 mycelium, of many different forms, though constant within narrow limits in 

 a given species. Inside the usually reticulated conceptacles there are 

 attached to the base one or more sporangia or spore-sacks. These are thin 

 and transparent, showing plainly the few or many spores. Sometimes, in- 

 stead of sporangia, multitudes of naked and smaller spore-like forms are 

 found ; and sometimes similar ones are contained in a stalked flask-shaped 

 or urn-shaped vessel, as seen in Plate III, Fig. 7. Still other apparent 

 fruit-bodies are found on the mycelium or the appendages of the conceptacles. 

 I do not remember seeing these described, but have often met them and am 

 fully convinced that they belong to the same plants. They are dark- 

 colored like the Dematiei species, and of the forms shown in Plate III, Figs. 

 2b, 2c, 2d, 7f, and Plate IV, Fig. 12. Save in quantity, they are not 

 unlike forms of the black mildews found on thick-leaved plants and known 



