10 FAELOW ON THE GYMNOSPORANGIA 



near the surface have short promycelia, while those of the interior have very long ones, 

 the object evidently being that the tips -syhich bear the sporidia may reach the light and 

 air. 



One of the most curious and interesting phenomena connected with the growth of Gym- 

 nosporangia is the peculiar distortions which they produce in the plants on which they 

 are parasitic. The mycelium does not differ much from that commonly found in the other 

 Uredineae. It is irregular, much bi'anched, and cross partitions are rather numerous. Un- 

 like, however, the mycelium of some of the Pucciuiae, that of the species of the present 

 genus is limited in extent, and is not found throughout the whole of the plant on Avhich it 

 is growing, but is confined to certain portions of the stems or leaves. The mycelium of 

 most of the species is perennial, that is, the mycelium which has produced a crop of 

 spores one year, will the next year, under ordinary circumstances, produce another crop in 

 or near the same place. One species, however, and possibly others are annual, the spores of 

 one year not following those of another in the same place. The kinds of distortion pro- 

 duced vary with the species, but it is probable, although not absolutely certain, that the 

 same species produces difierent deformities when growing on different species of plants. 

 This we might jierhaps account for by a difference in the histological character of the two 

 plants, but exactly why two different species of Gymnosporangium parasitic on the same 

 individual cedar, should produce two widely distinct deformities is less easily explained. 

 In the mere appearance of the mycelium itself, one can not see any cause for the different 

 growths j^roduced. 



The explanation is evidently to be sought in the amount and extent of the mycelium, 

 the rapidity of its growth, and its duration. Thus in a rapidly growing annual species, as 

 G. macropus, we have a large, rather spongy excresence which shrivels in drying. In O. 

 fuscum var. glohosum, which is perennial, and of slower growth, the excrescence is more 

 dense and scarred externally. In G. biseptatum the mycelium is comparatively limited in 

 amount, and does not increase rapidly, and in consequence, the formation of the annual 

 woody layers is not prevented, nor the nutrition of the branches above much interfered 

 with. The mycelium is found principally in the region of the cambium, and acts rather 

 as a stimulant than as a destructive agent, and the result is that a nodose swelling is formed 

 in consequence of the unusual development of the wood in the region of the fungus. 

 In G. Ellisii, which like the previous species, grows on Ciqjressus thyoides, there is a 

 more luxuriant and rapidly growing mycelium, which extends for some distance along the 

 smaller branches, and is so abundant as to interfere with the nutrition and, in consequence, 

 the branches above become short and stubby, and, at length, densely fasciculated, the 

 branch below the fungus remaining unchanged, so that we have, instead of a nodose swel- 

 ling, a dense tuft of short branches borne on the end of a normal branch. In other 

 species the mycelium traverses the leaves, which are distorted throughout, so that the 

 branches infested by the fungus and those free from the fungus, seem to belong to differ- 

 ent species, so regular is the hypertrophy of the leaves. In this connection it may be 

 remarked that in some places the distortions are not altogether due to the direct action 

 of the fungi themselves, but are produced in part by the secondary action of the disor- 

 dered nutrition combined with the effect of the weather. Nor can one infer from the 



