1887] Botany. n 15 



destroyed, and they become brown and dry, as in many species 

 of Septoria, or crumble and fall out, leaving holes in the leaf, as 

 frequently in Puccinia asteris. Where the injury is not so severe, 

 spots of various colors, often characteristic of the species, mark 

 more or less definitely the extent of the mycelium. Exposure 

 to light and the activity of the chlorophyll may be lessened in 

 another way, by a change in the position of the infested stems 

 and leaves. A very common effect of a parasite is a more erect 

 and rigid growth, as in blackberries diseased with Cceoma nitens, 

 the orange-rust, and in the garden spurges, Euphorbia maculata 

 and E. hypericifolia, infested with the cluster-cup, JEcidium eu- 

 phorbia. These spurges normally grow prostrate, with leaves 

 widely spreading, allowing the greatest possible exposure to 

 sunlight. In the diseased condition the stems are erect and the 

 leaves less favorably spread. 



(3) Growth may be abnormally accelerated or retarded, and 

 both these effects may be produced in different cases by the same 

 fungus. Peronospora parasitica growing upon the common pep- 

 pergrass, Lepidium virginicuni, forms a thick, felted coating of 

 hyphae upon the under surfaces of the leaves, and causes the 

 latter to be somewhat contracted. The same fungus growing 

 upon the stems of Sisymbrium canescens causes swelling and 

 distortion. The ^Ecidium on Sambiicus canadensis distorts the 

 stem by accelerating growth, the infested side becoming swollen 

 and the stem bent. 



Exobasidium vaccinii on species of Vaccinium causes the leaves 

 to shrink ; forms believed to belong to the same species, growing 

 on Azalea and Andromeda, produce inflated sacs, often several 

 inches in diameter. 



A distortion usually consists of the fungus producing it and 

 the abnormal tissues of the host, as illustrated in the smut of 

 maize and the curl of peach-leaves. In the latter extra layers of 

 cells are formed on one side. 



yEcidium euphorbice accelerates the growth of the stems of its 

 host and retards that of the leaves, — an effect resembling that of 

 insufficient light upon plants, as upon vines on the shaded side 

 of a trellis, or potato-sprouts in a cellar. The orange-rust on 

 blackberries retards the growth of the leaves, as does also the 

 cluster-cup upon Ranuncu/us abortivus. 



Fusicladium, the scab-fungus of apples and pears, retards the 

 growth often of one side, while that of the other continues, pro- 

 ducing unilateral development and curvature of the axis of the 

 fruit. 



(4) Fungi are not confined to the chlorophyll-bearing parts of 

 plants ; woody stems, roots, flowers, seeds, and fleshy fruits all 

 have their parasites. One of the Myxomycetes, Plasmodiophora 

 brassicm, causes the disease called club-root in the roots of 

 cabbage. The appearance of the club-root of roses, which is 



