ON THE FRUCTIFICATION OF RHYTISMA MAXIMUM. 29 



erumpent, tlie blackened patches and tlie cuticle being incorporate. 

 ]\Iodifications in structure now take place wliicli result in tbe deve- 

 lopment of asci beneath the blackened cuticle, in the vacuity which 

 originally contained the spermatia ; when this is the case the 

 blackened cuticle becomes adherent to, and forms an outer covering 

 for, the ascigerous layer, giving the plant a black, shining, smooth 

 surface. As the plant develops, the surface becomes more or less 

 cracked in various directions, and the asci thus exposed. 



Sometimes, however, the plant is truly erumpent, and from the 

 first* of subcutaneous origin. It can readily be recognised as a 

 thickening of the bark before the cuticle ruptures ; in this state 

 the yellow circumference is usually absent. In whatever manner 

 it arises the ascigerous stratum is always of a whitish colour, con- 

 sisting of an assemblage of cylindrical octosporous asci t. 53, f., 

 3 and 4, containing ovate, very pale yellow sporidia, each of which 

 when young is enveloped in a thin gelatinous vestment, and filled 

 by a granular endochrome, with one or more large nuclei. They 

 measure some -0013 x "0003 in. upon an average. The paraphyses 

 are abundant, filiform in outline, very slightly incrassated above, 

 also containing granules, but we have never been able to see any 

 distinctly articulate bodies, such as Tulasne, t, xvi, f. 6, repre- 

 sents. As the plant matures, it separates at the edges from the 

 matrix, becomes revolute, and finally falls off, leaving a smooth 

 cicatrix, formed by the exposure of the inner bark. 



We also meet with reproductive bodies of two other kinds, 

 namely a Ftisarium, which oozes out upon the surface of the Rhy- 

 tisma in little roseate masses. These consist of curved spores, 

 obscurely triseptate when mature, which were originally borne 

 upon little threads, t. 53, ffg. 8 and 9. 



The other bodies are spores having some resemblance to those 

 belonging to the genus Hendersonia^ dark brown in colour, from 

 •0007 in. to '0009 in. long, usually triseptate, but occasionally 

 with four transverse, and one longitudinal septa. They are 

 developed from the interior of a somewhat indistinct perithecium, 

 imbedded in the Rhytisma, and originate as simple hyaline oblong 

 spores, which acquire first one septum, then the other two, and at 

 last the coloured endochrome (t. 53, f. 5.) The perithecia have a 

 minute shining black ostiolium, which is visible on the surface of 

 the Rhytisma. We have only found the ascigerous fungus in 

 spring and early summer, but the Rhytisma is to be met with at 

 all seasons. Hence we conclude season has a good deal to do with 

 the determining the exact mode of reproduction. Frequently we 

 have examined plants, and have found the white stroma, but no 

 trace of spermatia or asci ; it is under these conditions that the 

 Fusarium spore are most likely to be met with, and later on tlie 

 Hendersonia spores. This species of Rhytisma differs from ita 



* See Grev. t. 206, fig, 1, where a small branch is depicted distinctly repre- 

 senting this. 



