Smuts ill their Relation to Rusts- 43 



Th ' alternation of gonoiations in tlie Rusts may be thus graphically 

 represented : — 



Conidi 



Saprophytic Si)oro])liyte h ■^"*^ Gamctopliyte (.Myceliiun). 



(Pro mycelium). 



Ae:'idio-Ureclo- and \^5 ^J Gametes (Uninucleate). 



Teleutosporeir 

 Parasitic 8i)oro])liyte. Vi 3/ Fertilized Cell (Biniuleate). 



In both smuts and rusts there is a tendency to dispense with the sapro- 

 phytic stage, and become more perfect parasites, as, for instance, in the species 

 of smut infecting the host through the flower, and Puccinia (jraminis in 

 Australia dropping this stage altogether. 



Alternation of Parasite and Saprophyte. — Only one kind of reproductive 

 body is formed inside the host-plant, and these smut spores are produced 

 by the j)arasitic form of the fungus. When these spores are set free and 

 scattered by the wind or other agency they may either immediately, or after 

 a period of rest, begin to germinate. This process of germination takes 

 place outside the host-plant, and gives rise to a promycelium which generally 

 produces conidia, either laterally and terminally, or only at the apex. 

 Germination readily occurs in a mitrient solution, and since the formation 

 of conidia has been carried on by this means from generation to generation 

 for more than a year, as in the oat smut, this must be regarded as the sapro- 

 phytic form of the fungus. In some instances, as in Tilletia, when food 

 material is abundant, the promycelium is not limited to a short germinal 

 tube, but grows into a large branched mycelium like a tuft of mould, which 

 bears conidia, differing slightly from those produced normally. While in 

 the rusts two different host-plants are often concerned, in the smuts there 

 is only one, but a saprophytic mode of life succeeds and alternates with the 

 parasitic mode of life. During the parasitic stage, there is a definite form 

 of spore produced which is capable of giving rise to conidia on a germinal 

 tube, and in the saprophytic stage the conidia formed are capable of sprouting 

 continuously, as long as the nutriment lasts, and then putting forth a germ- 

 tube which penetrates the living plant if it comes in contact with it at the 

 right stage. In the one case the living and the dead substratum exerts an 

 influence which results in the different reproductive bodies, in the other it is 

 the living substratum of different host-plants which produces the variety 

 of spore forms. The researches of Klebs^ already referred to, show that it 

 is just this exhaustion of food in the successive host-plants attacked which 

 brings about the different reproductive bodies. 



The rusts have an advantage over the smuts in the variety of spores 

 produced, and their appearance at different seasons of the year. Not only 

 have they reached the highest degree of specialization in the selection of their 

 host-plants, often confining their attention to one particular species, but 

 they may select one plant for the production of spring spores and another 

 for summer and winter spores, so that their distribution is increased and 

 their adaptation to varying climatic conditions improved. 



Aeci'lia-like Forms. — In the higher forms of smuts there is an approach 

 to the aecidia of the rusts, and the characters of Doassansia and Cintractia 

 are very suggestive in this connexion. In Doassansia the fertile spore- 

 clusters are enclosed in a peridium formed of closely packed sterile cells, 

 arranged in a single layer. In Cintractia the spores arc developed in rows, 



