Origin of Spore-forms. 33 



The sporidiolum was thus at first the product of a basidium arising 

 from a mycelium, but there was nothing specially characteristic in this, nor 

 any advance upon the mode of reproduction in a saprophytic f ungus'. That 

 which constituted the Rusts a distinct class, and separated them from their 

 nearest allies, was the development of a new kind of spore, the teleutospore, 

 which produced directly on germination, without the intervention of any 

 mycelium, a basidium bearing sporidiola. In the one case the sporidiola 

 were derived from a basidium borne by a mycelium nourished on dead or 

 decaying matter ; in the other the basidium, or so-called promycelium, was 

 the direct product of a living spore. This spore is the special feature of 

 this group of parasitic fungi, and will now be considered. 



TELEUTOSPORE. 



In the sporidiolum the fungus is provided with a spore capable of 

 germinating at once and reproducing the original form, but a parasitic 

 fungus requires further to accommodate itself to the varying seasons of 

 growth of the host-plant, and so a spore that could persist during the 

 winter while vegetative activity was practically suspended, became a neces- 

 sity. Hence the teleutospore, or typical resting- spore;, was introduced into 

 the cycle to provide a thick-walled form, which could withstand the vicis- 

 situdes of climate and be ready to germinate when spring, with its revival 

 of growth, returned. While some teleutospores are capable of immediate 

 germination, the great majority undergo a period of rest, and a thickening 

 of the wall is associated with this condition. 



While the sporidiolum was thus 1 probably the earliest-formed rust spore, 

 it did not meet all the requirements of the new mode! of life, and thus the 

 teleutospore became a necessity for parasitic life, a condition dependent on 

 the changes of a living organism. The great feature of a teleutospore is 

 the mode of germination and its product, and perhaps the simplest form 

 is represented by that of Bar clay ella Diet, in which there are several cells 

 in a row, and each cell produces a promycelium or septate germ-tube. The 

 peculiarity and primitiveness of this promycelium lies in the fact that, 

 instead of dividing transversely and each cell giving rise to a sporidiolum, 

 the promycelium itself breaks up into four divisions, each of which becomes 

 a sporidiolum (Fig. 12). 



FIG. 12. 



The only species belonging to this genus occurs on a Conifer (Pice a 

 morinda Link) in the Himalayas, and neither uredospores nor aecidiospores 

 are known. It produces the most primitive form of teleutospore, and the 

 geim-tube produced from each cell breaks up directly into sporidiola, which 

 again reproduce the fungus. This is an evident contrivance for multiply- 

 ing the spore-form (teleutospore) and providing a fresh start with a 

 sporidiolum, minute, light, and easily transported by the wind. 



The next advance in the development of the teleutospore may be seen 

 in an interesting genus, just described by Arthur 6 , to which he has given the 

 name of Baeodromus. It occurs on Senecio, and resembles Coleos-porium 



