MONOGRAPH OF TliE LAliOULBENIACE^E. 



359 



This well-defined and characteristic genus was first described by me under the name Acan- 

 thomyces, in ignorance of the fact that it had already been used by Lebert in a zoological 

 paper (Zeitschrift fur Wissenschaftliche Zoologie, 1858, Vol. IX., p. 447) for an entomogenous 

 fungus probably identical with Isaria xphingum. The name Rhachomyces has been substituted 

 as suggesting the resemblance which tbe main axis of the plant bears to a vertebral column, a 

 resemblance sometimes made more striking by the presence of a sigmoid curve (Plate XII, 

 fig. 6). 



The eight species which compose the genus are very constant in their essential characters, 

 and vary chiefly as regards the number of cells composing the main axis of the receptacle, and 

 in the number and length of the appendages. Extremes in these respects are represented by the 

 two species R. pilosellus (Plate XII, figs. 12-13) and R. longissimus (fig. 4). I have been unable 

 to obtain a series of young specimens to illustrate the complete development of the main axis of 

 the receptacle ; but from the specimens available it is evident that the main body of the latter 

 arises as a lateral outgrowth, somewhat in the same manner and in the same position that the 

 perithecium of genera like Laboulbenia or Stigmatomyces originates. The youngest condition 

 observed consists of a simple series of superposed cells, the terminal portion of which, all above 

 the sub-basal cell, becoming blackened and modified to form the lowest member of the series of 

 appendages, which are characteristic of all the species of this genus. It is then as an outgrowth 

 from the sub-basal cell that all the remainder of the plant is developed. The first indication of 

 this development is seen in fig. 10, Plate XII, in which an oblique partition has divided the sub- 

 basal cell into an upper and a lower portion, and it is from the subsequent divisions of this upper 

 portion that the body of the receptacle, including the male and female organs, arises. The axis, 

 as in so many other instances among the Laboulbeniacea?, more especially in the case of their 

 appendages, seems to consist in reality of a series of sympodial branches, while the appendages 

 and antheridial branchlets arise from small cells, which become laterally separated on one side. 

 The appendages are arranged in two vertical rows throughout the greater portion of the axis, 

 thus succeeding one another in pairs as a rule ; and between them and for the most part wholly 

 concealed by them are borne sterile or antheridial branchlets ; the latter, so far as known, also 

 produced in pairs, appressed in habit, each bearing a single terminal, flask-shaped antheridium 

 of the usual form (figs. 18-19). The perithecium seems to arise from one of the sub-terminal 

 cells of the main axis between the appendages, which may at maturity be present around its 

 base. The terminal portion of the axis often extends normally some distance beyond the base of 

 the perithecium, as in R. f urcatus ; while in other cases it may be very short, as in R. lasio- 

 phorus ; and it is from this portion that the proliferation described below takes place. 



The receptacle normally bears but a single perithecium, but in exceptional cases two may be 

 formed side by side from the same cell (Plate X, fig. 22). When, however, the trichogyne has 

 for any reason failed to become fertilized, or the perithecium which was first formed is injured 

 or becomes infertile, a terminal proliferation of the axis takes place, and from this proliferation 

 is produced sub-terminally a second perithecium, as in fig. 2, Plate XII. This process may be 

 once or even twice repeated, as in fig. 14 ; but in any case the phenomenon is not to be con- 

 sidered a normal occurrence. It may be mentioned as a curious fact that the number of cells 

 which compose one of these proliferations in a given species seems to be more or less constant, 

 as indicated in the figure last cited. 



