OF THE UNITED STATES. 



9 



sted the aecidial stage is found in the so-called Roesteliac which are found on different 

 species of Pomeae but no indications of a uredo-stage have as yet been detected. 



An acquaintance with some of the more recently discovered American species shows 

 that the original limits of the genus must be extended so as to include species in which the 

 spores become several (3-G) celled, and in which the amount of gelatinous substance found 

 is comparatively small. In other words, as far as can be judged from the teleutosporic 

 condition, the genus evidently approaches Phragmidium in G. Ellisii, which species can- 

 not well be placed in a separate genus, as was done by Kornicke 1 in forming his genus 

 Hamaspora. The teleutosporic condition of Gymnosporangium unlike that of most of 

 the other genera of Uredineae of temperate regions, is found in the spring, and the species 

 of the United States occur only on species of Juniperus, Cupressus, and in California on 

 Libocedrus. The production of the promycelium and sporidia is seen with the greatest 

 ease and, in fact, after a shower the orange-colored masses are covered with the latter. 

 When, however, the masses after having been wet are quickly dried, instead of a produc- 

 tion of sporidia from the promycelium, the latter divides quickly into a number of cells 

 which separate from one another, and which on remoistening send out germinal tubes just 

 like the sporidia. A similar transformation of the promycelium was noticed by Cramer, loc. 

 cit., p. 7, in Gymnosporangium fuscum growing in Switzerland. In the Northern States 

 the teleutospores make their appearance usually from the middle of April to early in May 

 according to the season, reach perfection in May and disappear at the end of June. In 

 the South they are found considerably earlier. 



The principal characters used in distinguishing the species are the shape and size of the 

 gelatinous masses, the shape and size of the spores, and the number of cells of which they 

 are composed, the number and position of the promycelia produced from each cell, and the 

 form and character of the swellings or distortions produced in the plant on which they are 

 parasitic. The particular shape of the gelatinous masses in any given species depends con- 

 siderably upon the age and amount of moisture, and in all species, after having been repeat- 

 edly expanded by numerous showers and again dried, they become amorphous. When first 

 appearing after the rupture of the epidermis, or outer bark, they are in the form of cush- 

 ions of a dark velvety color. As they reach perfection, the forms they assume may be divi- 

 ded into three ; the cylindrical, which may be either blunt or acutely attenuated ; the 

 flattened or wedge-shaped, which are usually blunt and crenate or partly divided ; and the 

 irregularly expanded, which are broadly ovate or flattened and generally plicate. The 

 usual number of cells is two, but even in species which normally have only two cells, one 

 sometimes finds three or four cells. The single-celled spores are generally immature, but 

 occasionally they bear promycelia. In two of our species the normal number of spores is 

 greater than two. The number and position of the promycelia given off from each cell 

 varies considerably in the same species. As a rule, they are not borne at the apex of the 

 cells, but near the line of union of two cells. They are occasionally produced from the 

 apex, and in one species, that seems to be the common position. In some species the usual 

 number of promycelia to each cell is four, in others only one or two. The length of the 

 promycelia depends upon the position of the spores in the gelatinous mass. Those on or 



1 Hedwigia. 



Vol. xvi, p. 22. 



1877. 



