178 



BOTANY 



spores only are developed, and these germinate as soon as they are 

 ripe. From each of the two cells, a short tube (Basidiuin, Proniy- 

 celium) is sent out, into which pass all the spore-contents. The 

 basidium divides usually into four cells. Each of these develops a 

 single sterigma, which swells at the end, and forms the single spo- 

 ridium into which all of the contents of the basidial cell pass. The 

 sporidium germinates at once, sending out a short tube which prob- 

 ably, as in other cases 



A .-- /vJv\TX observed, enters the 



host through a stoma. 

 Gymnosporangium. 

 Of the hetercecious 

 Rusts, one of the most 

 striking is Gymnospo- 

 rangium, of which there 

 are several species caus- 

 ing the " Cedar-apples," 

 gall-like excrescences 

 (Fig. 144) upon the 

 twigs of the Juniper 

 and Red-cedar. If these 

 galls are examined in 

 the early spring, the sur- 

 face shows slight eleva- 

 tions, beneath which 

 masses of young teleu- 

 tospores may be found. 

 As these mature, they 

 burst through the epi- 

 dermis and appear as 

 little orange-colored 

 spikes (Fig. 144, A). 

 These consist of masses 



FIG. 144. Gymnosporangium macropus. A, " Cedar- 

 apple " upon Juniperus Virginiana, with young 

 masses of teleutospores, sp. (Natural size.) B, 

 two teleutospores; in one the promycelium, pr, has 

 begun to grow. C, promycelia, with sporidia, x. 

 D, leaf of Cratsegus crus-galli, with the aecidium 

 (Roastelia) of Gymnosporangium. 



of two-celled spores borne upon long stalks, which are of gelatinous 

 consistence, and swell up into large masses of soft, orange-yellow 

 jelly, when they are wet. Spores taken from such a mass may be 

 found germinating, much as those described for the Mallow-rust. 

 Sometimes, instead of forming sporidia, the promycelium divides 

 into joints which separate as single spores. 



The sporidia germinate promptly, but will not infect the Cedar. 

 If placed upon the young leaves of Apple or Hawthorn, however, 

 the germ-tube will penetrate them, and in the course of a few weeks 

 there will be produced orange-colored, somewhat thickened spots, 

 upon whose upper surface the black spermogonia are borne; upon 

 the lower side, the secidia appear, which were first described under 



