161 



NOTES ON MYCETOZOA. 



By Aethur Lister, F.L.S. 



(Plate 386.) 



Physarum didermoides Eost. var. liyidum, n. var. (PL 386, 

 fig. 4). In searching for the various forms of Mycetozoa, we have 

 until recently confined our attention very much to old stumps and 

 fallen leaves in woods and gardens ; during the last year, however, 

 Mr. Saunders, of Luton, and Mr. Crouch, of PuUoxhill, Beds, have 

 found that straw-heaps that have lain long undisturbed yield 

 species of the genera P/njsaruui. and Didymimn, often in vast abund- 

 ance, and of special interest. In April, 1897, Mr. Saunders sent me 

 a specimen presenting unusual characters, which he had gathered in 

 a deserted stackyard on an exposed hill-top on the Dunstable Downs. 

 A few days later my daughter and I visited the spot in his company, 

 we found the wet straw beneath the dry superficial layer covered 

 with the sporangia of Mycetozoa, principally of Didytnium effumm 

 Link, and D. difforme Duby, but also with a large growth of the 

 form we specially came in search of. Ii is a Physarum. with the 

 following characters : — Plasmodium white ; sporangia subglobose 

 or ovoid on a broad base, 0*5 to 0-6 mm. diam., sessile, crowded, 

 grey, and somewhat rugose from deposits of lime, or purplish- 

 iridescent from the absence of lime, exceptionally white with a 

 densely calcareous wall ; they are either seated directly on the 

 straw, or on a thick white hypothallus devoid of refuse matter, and 

 sometimes extending beyond the sporangia in smooth white folds ; 

 the sporangium- wall is generally single and membranous, with 

 innate deposits of white lime granules, but in some parts of several 

 gatherings it is double ; the outer layer is white and densely cal- 

 careous, here and there separating fiom the membranous nnier 

 layer ; the latter is usually colourless, but sometimes purplish and 

 Avrinkled ; columella none ; capilhtium consisting of numerous 

 white lime-knots, rounded or irregular in shape, connected by 

 rather short, sparingly branched, hyaline threads; the spores 

 measure 10 to 12 /x, and are very dark purple-brown, strongly but 

 not very closely warted on two-thiris of the surface; over the 

 remaining third the spore-wall is thinner and paler, and the warts 

 more scattered (PI. 386, fig. 4). Other gatherings with precisely 

 the same characters were obtained at GhaulEnd (the source of the 

 April discovery) in June, 1897; at Barton, some miles distant; 

 and at Nether Crawley, in October, 1897 ; in this last the spores, 

 though very dark, are a shade browner, paler and more uniform in 

 colour. The dark spores and characteristic capillitium suggested 

 that in these gatherings we had a form of P. didermoides, but the 

 sessile sporangia agreed with Rostafinski's description of P. lividmn. 

 The typical form of P. didernwides'Rost. has erect ellipsoid sporangia 

 with white membranous stalks rising from a well-developed white 

 hypothallus, a capillitium with numerous rounded lime-knots, and 

 purple-brown, almost black, spores. Rostafinski's description of 



Journal of Botany.— Vol. 36. [May, 1898.] n 



