42 



Smuts in their Relation to Rusts. 



saprophytes which are occasionally parasitic, and parasites which are 

 occasionally saprophytic. In the case of grey mould {Botnjtis) and blue 

 mould {PeniciUium) we see parasites in the making, as it were, for they are 

 able, under certain conditions, to enter the living plant and grow there as 

 ordinary parasites. It is not so well known, however, that there are also 

 true parasites, which spend a portion of their existence outside the host- 

 plant, and, not only so, but saprophytic and parasitic stages regularly alternate 

 in their hfe-histor3^ 



The smuts were originally entirely saprophytic, and this stage is still 

 represented of course in a much reduced form in the promycelium bearing 

 conidia. The promycelium is all that remains of what was once probably 

 a much more elaborate organism. Next, they became educated up to and 

 developed into the parasitic stage, and this gradually took the lead, until now 

 it is the most conspicuous form, and is represented by the internal mycelium 

 bearing spores. Only one kind of spore is produced, but by means of nuclear 

 fusion, which serves the purpose of a sexual act and foreshadows it, it is 

 invigorated and rejuvenesced. There is here an alternation of a saprophytic, 

 with a parasitic stage, and it may be represented graphically thus : — 



Parasitic Sporophyte (Internal Mycelium). 



Conidia or Sprouting Conidia. M 2J Spores, 



Saprophytic Sporophyte (Promycelium). 



The earliest alternation was that of nutrition, as represented by a 

 saprophytic and a parasitic mode of life, and this gradually developed into 

 an alternation of spore-forms, using the term spore in its widest sense. The 

 parasitic form ultimately developed into a sexual form, so that an alternation 

 of a sexual with a non-sexual generation arose. 



With the development of sexuality a higher plane was reached, and greater 

 variety in the reproductive bodies secured, each specially adapted for 

 different conditions, and ultimately for different host-plants. This was the 

 starting point of the new group of rusts. It is interesting to note, in this 

 connexion, that Christman holds that the teleutospores are the primitive spores 

 of the rusts, and that the other kinds have been gradually intercalated in 

 their life-history. There is here, as in higher forms, a distinct alternation of 

 a sexual and asexual stage. 



The sexual stage is represented by an internal mycelium bearing sexual 

 cells or gametes, the contents of which blend and produce the fertiUzed 

 cell. 



The asexual stage is the product of the fertilized cell, and is represented 

 by the aecidisopores with their intercalary cells, and the mycelium produced 

 by them bearing uredospores and teleutospores. This is the parasitic form 

 of the sporophyte, which sometimes completes the cycle by the teleutospore 

 directly infecting the host-plant and producing a mycelium bearing the sexual 

 cells. 



But, generally, the saprophytic form of the sporophyte asserts itself, by the 

 teleutospore producing a promycelium bearing conidia, and the conidia 

 infecting the host-plant. 



