INTRODUCTION 15 



is sprinkled over with a deposit of crystals of lime, and after 

 being revived the cyst-walls are not dissolved as in Badhamia, 

 but remain as empty hyaline sacs when the contents have 

 <?rept out. The formation of sclerotium in plasmodia inhabiting 

 the interior of rotten wood is less easy to follow, but it is 

 probably of frequent occurrence. A plasmodium of Stemonitis 

 fusca, cultivated from spores in a moist chamber, passed into 

 the resting state a few days after it had formed, spreading in 

 a single layer of crowded cysts on the surface of the glass. 

 This sclerotium was dried and re-wetted, when it revived, 

 and the cyst-walls were dissolved ; the cultivation was con- 

 ducted with pure water, with no attempt to supply nourish- 

 ment, and the plasmodium returned to the encysted condition 

 in about twenty-four hours ; it was again dried and again 

 revived, but afterwards it reassumed the sclerotium state, 

 from which it could not be reawakened. 



The Sporangium and Sporophore. — The formation of the 

 sporangium in the Endosporeae has been minutely described 

 by de Bary,* and a brief notice of the general characters 

 will be sufficient here. The plasmodium usually leaves the 

 moist surroundings where it has been feeding and creeps 

 to some drier place more suited to the dispersion of the 

 spores. It concentrates at certain points and develops 

 into sporangia of the forms characteristic of the species. 

 They are either simple, though often densely clustered, or 

 they are combined into an aethalium, a cushion-like structure 

 consisting of numerous convoluted or imperfectly-defined 

 sporangia. The simple forms are either symmetrical, 

 with or without a stalk, or they are unsymmetrical, 

 spreading on the substratum with an irregular outline, 

 when they are called plasmodiocarps. In most cases 

 the shape of the sporangium is nearly constant, though 

 in others it is subject to much variation. Two abundant 

 species, Physarum nutans and Didymium squamulosum, may 

 be mentioned as examples of variable habit ; in each of them 

 we often find vein-like plasmodiocarps, and symmetrical 

 sporangia both stalked and sessile resulting from the same 

 plasmodium. It is true of the shape of the sporangium, 

 as it is of the size of the spores and the form and colour of 

 the capillitium, that though a valuable guide, it cannot be 

 taken as supplying a rigid specific character. The want of 

 a sufficient series of specimens showing how widely a species 

 may vary, has led to the multiplication of names without 

 adequate grounds. 



In examining the rising sporangia of Physarum nutans in 

 a moist chamber under the microscope, the projecting masses of 

 Plasmodium are seen to pulsate, swelling or shrinking as the 



* I.e., 424. 



