34 Origin of Spore-forms. 



senecioms so much in general appearance, that it was at first regarded as 

 that species, but the teleutospore produces a regular promycelium, with 

 sterigmata and sporidiola, so that it well illustrates the transition from the 

 basitlia bearing sterigmata in Coleosporium to the typical teleutospore 

 with a promvoelium. The teleutospores are united into a solid mass and 

 are arranged in chains consisting of 5-8 cells in a series, and while Arthur 

 considers each cell as a teleutospore, the chain of cells might be regards 

 as a multicellular teleutospore. The spores germinate immediately and 

 the promvcelia, together with the four globose sporidiola, have bright 

 orange contents (Fig. 13). Closely related to this form is Chrysomyxa, in 



FIG. 13. 



which the teleutospore consists of a series of cells, and on germination pro- 

 duces promycelia of several cells, each of which bears a sterigma with 

 sporidiolum. In Melampsora the unicellular teleutospores form a compact 

 mass, producing promycelia of the typical form, and thus a teleutospore 

 may either consist of a simple cell or a series of superposed cells. 



A teleutospore is thusi a unicellular or multicellular spore, producing on 

 germination a promycelium, which dither directly breaks up into usually 

 four sporidiola or divides into four cells, each of which produces a 

 sporidiolum at the apex of a sterigma. There is one exception to this in 

 the genus Endophyllum, in which the promycelium is the product of an 

 aecidiospore, but this may be regarded as a case where the function of a 

 teleutospore has been transferred to a derivative form, the aecidiospore. 



UREDOSPORE. 



The view that the uredospore is probably derived from the teleutospore 

 is favoured by the variability of the latter in many species, and the grada- 

 tions which are found to occur. At first sight the differences between the 

 uredo and teleutospore seem so great as to be insurmountable, but there are 

 distinct transitional forms from the one to the other. The membrane of the 

 typical uredospore is covered with spines, and this is an evident adaptation 

 for the spore which germinates immediately and is short-lived, and the 

 characteristic spines serve to attach it to the surface of the host-plant in 

 order that germination may be successfully accomplished. Magnus 2 , who 

 inclines to the view that the uredospores have developed out of teleuto- 

 spores, shows that in Uromyces scutellatus (Schrank), Lev., a gradation 

 can be traced between the reticulate or tuberculate membrane of the 

 teleutospore and the finely tuberculate or echinulate membrane of the uredo- 

 spore. 



As to the thinning of the wall, there is also every gradation to be met 

 with from the thick brown membrane to the thin, almost colourless one. 

 The passage from the one to the other possibly took place through such a 

 form as the amphispore, a modified uredospore still capable of undergoing 

 a period of rest, and in Avhich the wall still retains its thickness, but there 

 are several germ-pores. They may resemble the uredospores in shape, 



