30 ON THE FRUCTIFICATION OF RHYTISMA MAXIMUM. 



allies R. salicinmi, and acerinum in not maturing its asci during 

 the winter as they do : but the stroma is developed in spring, and 

 bears asci in early summer. 



King's Lynn. Charles B. Plowright. 



Plate 53. — Fig. 1. Rhytisma, nat. size. 2. Section of ditto 3. Ascus and 

 Bporidia X 500. 4. Sporidia X 500. 5. Pjcnidia resembling Hendersonia. 

 6. Free conidia. 7. Conidia on sterigmata from Tulasne. 8. Fusiform stylo- 

 ppores. 9. The same when free. 



CLASSIFICATION OF PYRENOMYCETES.* 



Several advances have been made by Continental Mycologists 

 of late years, towards a carpological classification of the Ascomy- 

 cetes. Some objections have but recently been stated by the writer in 

 the " Popular Science Eeview ;"| and the last volume of " Trans- 

 actions of the Woolhope Club," includes some observations by Mr. 

 C. E. Broome on the same subject. Professsor Saccardo's recently 

 published scheme affords an opportunity for a further consideration 

 of the basis of the classification proposed. Whatever may be the 

 merits of Professor Saccardo's scheme, these must be subsidiary to 

 the main question whether the basis is a sound one, and on this 

 point we have already expressed a very decided opinion. The sys- 

 tem adopted by Fries, with some minor modifications which expe- 

 rience has suggested, is based mainly on the vegetative system. 

 External features, which can be determined often by the unaided 

 eye, usually by means of a pocket lens, and only very rarely, and in 

 peculiar instances, by resort to the low powers of a microscope, 

 must commend itself, other conditions being equal, to the mycologist. 

 It surely must be preferable to adopt a system by means of which 

 an individual plant can, with little doubt or hesitation, be at once 

 referred to its correct genus, leaving to microscopical examination 

 its specific features, than to invert the order, and make microsco- 

 pical examination essential to the determination of the genus, whilst 

 external features are ignored. No one can doubt for a moment 

 how much the determination of a collection of new plants is faci- 

 litated by the ability to group them at once in their proper genera. 

 This is impossible with a carpological scheme, such as that proposed 

 by Saccardo. Experience has proved that Xylaria is a natural 

 and irreproachable genus, based on external features, on the clavate 

 or branched stroma, and without any regard whatever to the cha- 

 racter of the fruit. Because the sporidia are simple and coloured, 

 it may be in all known species, no attempt has been made to alter or 

 split up the genus, but its principal feature is not carpological. 



* Conspectus Gecerum Pyrenomyt-etum Italicorum, systemate carpologico'dig- 

 positorum, auctore. P. A. Saccardo. 

 t Pop. Sci. Eev., July, 1875, on " The Tendencies of Systematic Botany." 



