14 



MASS. EXPERIMENT STATION BULLETIN 183. 



Fig. 1. — Young mycelium 

 from culture. 



-Old mycelium, showing 

 chlamydospores. 



diameter. The manner of branching and septation is shown in Fig. 1. 

 When the myceUum is young the walls are thin and not constricted, or, 

 at most, only slightly constricted, at the septa. The contents consist 

 of homogeneous protoplasm. Both the walls and contents are colorless, 

 and when seen in 

 mass, in pure cul- 

 ture, look like white 

 cotton. But when 

 the mj'celium be- 

 comes older it be- 

 comes brown, the 

 hypha^ are gnarled 

 and twisted, deeply 

 constricted at the 

 septa, the cells short 

 and oval or globose, 

 giving one the im- 

 pression of strings 

 of beads (Fig. 2). 

 The cells now con- 

 tain large drops of 

 reserve food, and the walls are thick. These cells are probably more 

 resistant to adverse conditions, and serve to carrj^ the fungus through 

 unfavorable periods. They may be called chlamydospores. Their diam- 

 eter is much greater than that of the ordinary hyphre, as indicated by 

 the figures. 



SCLEROTIA. 



Sometimes the surface of old cankers is dotted over with minute shining 

 black pimples (Plate II.). They are usually not much larger than a pin 

 point and never as large as a pin head. 

 To the naked eye they look like pycnidia, 

 but microscopic examination always 

 proves them to be sterile balls of thick- 

 walled pseudoparenchjanatous fungous 

 cells (typical sclerotia). They are directly 

 under the epidermis, but this does not 

 obscure their shining black prominence. 

 In certain culture media they are pro- 

 duced in great abundance. The cells are 

 much like the chlamydospores; in fact, 

 the sclerotia seem to be only a further 

 development of the chlamydospore-forming hypha", and all gradations 

 between the two may be found. Their function is probably the same 

 as that of the chlamydospores. A thin cross-section of one is shown in 

 Fig. 3. 



Fig. 3. — Thin section through 

 sclerotium. 



