Smuts in their Relation to Rusts. 39 



however, show a step in advance by the characteristic whorl of conidia at 

 the apex of the jointed promycelium. 



According to this view, the smuts have given'_^rise to the Basidiomycetes 

 and form the connecting link with the Phycomycetes. But there are others, 

 such as MoellerandMassee, who assign a.different origin to the Basidiomycetes, 

 the latter regarding them as having originated independently from conidial 

 forms of the Ascomycetes. 



Having shown that the smuts are, probably, most nearly allied to the 

 primary group of the Basidiomycetes, let us now see in what relation they 

 stand to the rusts. The smuts are all parasitic fungi, mostly occurring in the 

 tissues of the higher plants, more particularly in the Gramineae, which are 

 often seriously injured by them. The spores are produced, as a rule, in the 

 interior of special or sporogenous hyphae, the walls of which become gelatinous 

 and finally deliquesce, while the protoplasm in the interior, develops into the 

 spores. When the ripe spores are thus set free, they germinate under the 

 influence of moisture, after a longer or shorter period of rest, or immediately. 

 The outer coat of the spore bursts at a particular spot and a germinal tube is 

 protruded, which ultimately divides by means of transverse septa into two 

 or more cells. As in the case of the rusts, this germinal tube is called a pro- 

 mycelium, and it bears the spore-like bodies or sporidiola here called conidia. 

 De Bary regards this germinal tube as of the nature of a mycelium, while 

 Brefeld considers it a basidial structure, and if we accept this latter view, then 

 the smuts, as well as the rusts, are akin to the Basidiomycetes. The whole ques- 

 tion turns upon what is meant by a basidium. A basidium is generally con- 

 sidered to be a relatively large cell giving rise at its apex to a definite number 

 of naked spores, which are produced only once at fixed spots. It must be 

 granted at once that the germinal tube or promycelium in the smuts has not 

 the definite characters of a true basidium. It is divided into several cells, 

 conidia may be produced laterally as well as terminally, and when they fall 

 away, new ones may be produced. But it may well be regarded, in its most 

 primitive form, as a transition stage to the more definite characters met mth in 

 the rusts. In the rusts there is a definite promycelium, consisting of four 

 cells, and each cell bears a single conidium or promycelial spore, which is 

 only once produced, although Brefeld* has shown that the conidia in the 

 smuts may sprout and produce secondary and tertiary conidia in a nutritive 

 solution. It may be considered as the variable form from which the 

 definite rust form has arisen. 



Not only was the product of the spore different from that of the rusts, 

 according to De Bary, but he pointed out that the snnits were essentially 

 different in the mode of formation of their spores. There, the contents of the 

 hyphae at certain definite spots are transformed into spores and the walls of 

 the sporogenoiis hyphae deliquesce and set them free, while in the rusts the 

 spores are pinched off from the ends of the hyphae. No doubt, this is a dis- 

 tinct difference, but when the sexuality of the rusts is considered and the 

 spores are seen to be the result of this, then a different mode of formation 

 was inevitable. 



But porliaps the most important difference between the two, according 

 to De Bary^* is the conjugating cells. He writes :— " If, on the other hand, 

 we look for the points which are distinctly characteristic of the Ustilagineae, 

 the most prominent is that of the conjugating pairs of cells." He considers 

 the pairing of the promycelial spores or conidia as of the nature of a sexual 

 act, but it is not now regarded as such, according to the present state of ki^ow- 

 ledge. It is simply a means of mixing the protoplasm from two different 

 sources, through anastomosis, and occurs in germ-tubes and hvphae as well. 

 This brines us to the Question, however, of true sexualitv in both. I have 



