1922] Notes on Sclerotium Rolfsii Sacc. 171 



systematic relationship 

 The presence of clamp connections and of the binucleate condition 

 in the mycelium shows the relation of the fungus to the Basidwmij- 

 cetes; but these characters are common to practically all the families 

 of this group. Sclerotia are also produced by members of nearly all 

 families of Basidiomycetes. It does not seem possible, therefore, to 

 determine with certainty any closer relationship until spore formation 

 has been observed. 



SUMMARY 



1. The presence of clamp connections and a peculiar method of 

 branching is a valuable aid in distinguishing the mycelium of 8. 

 rolfsii from that of other fungi producing similar lesions on plants 



2. The affinity of S. rolfsii to the class Basidiomycetes is indicated 

 by the septate, binucleate mycelium and by the presence of clamp 

 connections at the septa. 



3. The mixing of plus and minus strains is not necessary for the 

 production of sclerotia. 



Experiment, Ga. 



Explanation of Plate 29 



Fig. 1. Part of a sector from section of a very young sclerotium of S. rolfsii, 

 showing interwining of the slender hyphfe; a, the loose hairy covering; b, 

 darker stained growing region; and c, paler hyphae in the center of the 

 weft. X 367. 



Fig. 2. Part of a sector from section of a slightly older sclerotium; a, the 

 loose hyphal covering of the sclerotium; b, the pseudo-parenchyma with its 

 large cells and thick colorless walls; and e, looser growth and large air 

 spaces in the center of the sclerotium. x 367. 



Fig. 3. Portion of the outer tissues from a section of a mature sclerotium ; a, 

 remains of the loose hyphal coverings, partly dead and sloughing off; b, 

 pseudo-parenchyma, the outer layers of which have formed the brown cor- 

 tical coverings, x 367. 



Fig. 4. Section from near the center of a germinating sclerotium, showing two 

 slender new hyphae (d) pushing between the partly dead cells of the 

 sclerotial tissue ; from a scerotium more than a year old. x 367. 



Fig. 5. Septum and double clamp connections in vegetative mycelium of S. 

 rolfsii. X 154. 



Fig. 6. Portion of a hypha in which a branch lias grown out in the place of 

 one of the clamp connections, x 154. 



