Smuts in tJtcir Relation to Rusts. 



CHAPTER YII. 



Smuts in their Relation to Rusts. 



It has always been more or less generally taken for granted that there is 

 some sort of relation between the rusts and the smuts, but the exact nature 

 of that relation has never been definitely settled. On a superficial view, 

 there are seen to be black masses of spores produced in both cases, often 

 bursting through the particular parts of the plant on which they occur, which 

 suggest some close connexion, and even the farmer has been misled by this 

 superficial resemblance, for he invariably calls flag smut of wheat {Urocystis 

 tritici) " Black rust." 



On closer and deeper investigation, they are still found to have many 

 points of resemblance, so much so, that both were placed together by the older 

 writers under Fries' division of the Hypodermii. At the present time Brefeld'^ 

 who has studied the smuts more thoroughly than any other living investigator, 

 regards them as the progenitors of the rusts, and this genetic connexion is 

 supposed to be proved by various structures which they possess in common. 

 There was one jarring note, however, introduced to disturb the harmonious 

 relations which were supposed to exist between the two, and that was by 

 De Bary, as early as 1853. He considered that the rusts were very closely 

 allied to the Ascomycetes, while the smuts were more nearly related to the 

 Phycomycetes, but in order to understand the points of difference, as well as 

 the points of resemblance, it will be necessary to make a general review of 

 the position. 



There are three primary groups of fungi still generally recognised, which 

 are based upon purely morphological characters. The Phycomycetes or Alga- 

 like fungi are regarded as the primitive stock, and divergence has taken place 

 in two directions, the offshoots representing the other two main 

 divisions. The Ascomycetes are characterized by the ascus contain- 

 ing a definite number of spores, and the Basidiomycetes by basidia or large 

 terminal cells bearing naked spores at their free apex. 



Brefeld*^ has pointed out that, in the Basidiomycetes there are two dif- 

 ferent forms of basidia. In the one case, the basidia are septate, and a spore 

 arises from each cell, while in the other, they are undivided and bear at the 

 apex a definite number of spores, usually four. The most primitive forms 

 of basidia are divided transversely, hence called Protobasidia, and the un- 

 divided basidia are known as Autobasidia. In the smuts, the promycelium 

 arising from the spore agrees with the divided basidium of the Proto-basidio- 

 mycetes, but there is nothing corresponding to the undivided basidium of 

 the Auto- basidiomycetes, when fully developed forms are taken into con- 

 sideration. There are still some who strain analogy so far as to make the 

 promycelium of the Tilletieae correspond with an undivided basidium, but 

 the septa or divisions are just as pronounced in their promyceha when mature, 

 as in any of the Ustilagineae. The promycelia of the smuts are, therefore, 

 regarded by Brefeld as primitive basidia, foreshadowing the special basidia 

 of the Basidiomycetes, and the only point of difference between the two con- 

 sists in the promycelia of the former bearing a variable number of conidia, 

 while the basidia of the latter bear a definite number. The smuts are there- 

 fore called by Brefeld Hemibasidii, forming a sort of half-way house to the 

 Basidiomycetes proper, and they show their primitive nature, like the rusts, 

 bv representing the type in which the basidia are still divided. The Tilletieae, 



