Gcrmiiiaf'iou of Sforcs. 



CHAPTER V. 



Germination of Spores. 



The spores may either germinate in water or in a solution to which; 

 nutritive material has been added. The germination of spores in nutrient 

 solutions has been studied in great detail by Brefeld, and has been shown 

 to differ somewhat from that obtained when only water is supplied. The 

 first to employ nutrient solutions in studying the germination of smut spores 

 seems to have been Hallier- in 1868, who used a variety of substances, such 

 as starch paste, white of egg, milk, a solution of sugar, &c. In every case 

 where germination has been carried out by myself it was first tried in water, 

 and then usuiilv in some definite nutritive medium for comparison. 



The process of germination, wherever known, is given in connexion with 

 the various species, since it furnishes important systematic characters ; 

 but a general account is given here of the usual course of development. 

 When the spore begins to germinate under the influence of moisture, it puts 

 forth a longer or shorter germinal tube, known as a promycelium (Plate 

 I., m, n, 'p, r). Then small hyaline spore-like bodies are, as a rule, produced, 

 called promycelial spores or conidia (Plate I., q, s). In those cases 

 where infection of the flower takes place, as in Loose Smut of 

 Wheat, a much-branched mycelium is usually formed without any 

 conidia, and here we have an instance of the germinal tube developing 

 directly into a mycelium. 



When conidia are formed, they may directly produce a germ-tube which 

 infects the proper host-plant and develops a mycelium, which again reproduces 

 the spores. Or they may bud even while still attached to the germinal 

 tube, and give rise to secondary or tertiary conidia, which may in turn 

 germinate and penetrate the tissues of the host-plant. It happens not 

 infrequently that the conidia unite in pairs, even in some cases before they 

 have become detached from the promycelium. A short transverse tube 

 connects adjacent pairs, and the protoplasm of the two is placed in direct 

 communication. This pairing is regarded by De Bary as a sexual act — a 

 process of conjugation ; but Brefeld considers it as analogous to the 

 blending which takes place between different branches of a mycelium. 

 However that may be, after this union has taken place, a slender germ-tube 

 is produced which receives all the protoplasm from the paired cells, and can 

 infect the proper host-plant where it develops a mycelium, which in turn 

 produces a crop of smut spores. This may happen either with solitary or 

 paired conidia. While the spore follows the general course of development 

 sketched above when germination takes place in water, it is somewhat 

 dift'erent when a nutrient solution is supplied. Hallier^ observed that in 

 rich nitrogenous substances, such as white of egg, the germinal tubes were 

 thick and distorted, but he also considered that they changed into various 

 moulds from his cultures not being pure. It was Brefeld, however, who was 

 the first to successfully apply nutrient solutions to the prolonged and pure 

 culture of smut spores. He mostly used a sterilized decoction of fresh 

 horsedung, and found that when such a solution is employed the germina- 

 tion is not only more rapid and much more luxuriant, but that it can be kept 

 up indefinitely as long as nutriment is supplied and the reproductive bodies • 

 themselves are sometimes different. He soon found that water alone was- 



