1887] Botany. 11 17 



ises better practical results than this. The relations of a few of 

 the Uredineae are known, as are also the relations of Ustilagineae 

 and the yeast-like forms which may be looked for in manure ; 

 but of the life-histories of the great group of "Fungi imperfecti," 

 including many injurious species, almost nothing is known. 



It is often difficult to. estimate the extent of the injury to be 

 attributed to any one of these causes, as several commonly op- 

 erate together. Canada thistle attacked by Puccinia suaveolens 

 wilts in hot sunshine, while healthy plants remain fresh ; and 

 this appears to be due chiefly to the first cause, the loss of nutri- 

 ment, which weakens the physiological power. Is it possible 

 that the breaking of the epidermis by the sori, in this or other 

 cases, increases the rapidity of transpiration ? 



Farmers say the red rust of wheat produces comparatively 

 slight injury, while the black rust is destructive. The black rust 

 appears on the stems, which at that stage of growth have little 

 chlorophyll, even if healthy ; the formation of winter spores ap- 

 pears to make a greater drain upon the resources of the host than 

 the formation of summer spores, which have much weaker vitality. 



Certain groups of plants are the prey of certain groups of 

 fungi. Gymnosporangia grow upon Cupressineae ; Raesteliae upon 

 Pomaceae ; Phragmidia upon the sub-order Rosaceae proper. 

 Numerous species of Uromyces are parasitic upon Leguminosae, 

 and the grasses support more Pucciniae than does any other 

 family of phanerogams. In these two genera no species is 

 known to produce its teleutospores upon" host-plants belonging 

 to more than one order. The large majority of Uredineae grow 

 upon herbaceous plants, as do Ustilagineae and Peronosporeae. In 

 these groups a given species commonly inhabits but few species 

 of host-plants, while some Erysipheae inhabit a large number. 



Many Erysipheae grow upon woody plants. Fungi imperfecti 

 are perhaps least of all to be classified with reference to hosts, 

 though many of their genera may be. Woody plants have fewer 

 active parasites than herbaceous plants. Water-plants and those 

 of wet places are freer from attack than those which grow upon 

 common soil. 



To recapitulate, parasitic fungi injure their host-plants by (1) 

 depriving them of nourishment; (2) impairing the power of as- 

 similation; (3) abnormally accelerating or retarding growth, 

 causing distortion ; (4) not only green parts are affected, but 

 roots, stems, inflorescence, flowers, and fruit; (5) leaves and fruit 

 fall prematurely ; (6) decay is produced in ripe fruits before and 

 after removal from the plant; (7) valuable plants receive injury 

 from those of less value by ordinary infection or hetercecism. 



The amount of injury due to one cause is uncertain, since 

 several act together. 



Certain groups of phanerogams are liable to be attacked by 

 certain groups of fungi. — A. B. Seymour, Cambridge, Mass. 



Jan. 30, 1888. 



