40 Relation of Rusts to other Fungi. 



CHAPTER XII. 



RUSTS IN THEIR RELATION TO OTHER FUNGI. 



The Fungi, as a class, are generally regarded as having descended 

 from the Algae, but since the latter possess the green colouring matter 

 or chlorophyll which enables them in the presence of sunlight to abstract 

 carbon from the carbon dioxide of the air, they do not seem to be the 

 most primitive forms. But the fission-fungi, such as the nitrifying bac- 

 teria occurring in the soil, are able, in the absence of light and chloro- 

 phyll, to split up carbon dioxide and obtain the necessary carbon likewise 

 from inorganic material, so that the first forms of life to appear upon the 

 earth could thus obtain their nourishment without organic compounds at 

 all. The development of the chlorophyll would thus occur at a later 

 period, and the fungi proper, as well as the algae, may have had a common 

 origin from these primitive bacteria, instead of the one being a degenerate 

 form of the other. 



Following the fate of the fungi, with which we are more immediately 

 concerned, their course of development ran parallel with that of the algae, 

 so much so that they have, been regarded as degenerate algae or algae 

 without chlorophyll. This primitive stock resembling the algae so closely 

 is known as Phycomycetes, and from this divergence has taken place 

 in two directions, the offshoots representing two main divisions of fungi. 

 In the one case the Ascomycetes or fungi producing spores in delicate 

 sacs or asci, and in the other, the Basidiomycetes or fungi producing naked 

 spores on large terminal cells known as basidia. To this latter division 

 belong the Uredines or rusts, since they produce basidia which are trans- 

 versely divided, and bear naked spores ; but they occupy a low position 

 as compared with the higher Basidiomycetes, including the mushrooms 

 and toadstools. In the Ustilagines or smuts closely related to the rusts, 

 the basidia are not as yet definitely fixed, since the, spores are produced 

 at any part and new ones are developed when the old ones fall away, 

 which is not the case in the rusts. 



The following arrangement will show the position of the rusts in this 

 scheme of classification : 



Fungi. 

 ( Ascomycetes 



Phycomycetes (Alga-like Fungi) J B (Hemibasidii (Smuts) 



' j Basidiomycetes 4 Protobasidii (Rusts) 



[Holobasidii (Mushrooms, &c.) 



Starting from the Phycomycetes or alga-like fungi, there is one divi- 

 sion of them which bears both sporangia and naked spores, and another 

 in which the sporangia may be wanting. The former would give rise to 

 the Ascomycetes, and the latter to the Basidiomycetes, which exclusively 

 reproduce themselves by naked spores. 



The srnuts are generally regarded as stepping-stones from the Phycomy- 

 cetes towards the rusts, which have become more closely identified with 

 the true Basidiomycetes, where the basidia are entire and not divided. 



The above gives a very general idea of the position of the rusts among 

 the fungi, and indicates briefly, without entering into detail, how they 

 may have originated. 



The parasitic habit of the rusts will account for several features in 

 their life-history as well as in their structure. Being dependent on other 



