INTRODUCTION. 1 1 



being placed in water ; that which has been lately formed resumes 

 the streaming condition in a few hours ; when of greater age it 

 requires to be kept wet for some days before the movement 

 begins ; the cyst-walls are then absorbed, and their contents 

 coalesce. It frequently happens that parts of old sclerotia are 

 incapable of resuscitation, but they afford a pabulum for the 

 newly awakened plasmodiurn, through whose veins the cysts may 

 be seen to be carried along and broken up. The sclerotium of 

 Didymium effusum 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 has crept out. The formation of sclerotia in plasrnodia 

 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 sclerotinm was dried and re-wetted, when it revived, 

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

 with pure water, with no attempt to supply nourishment, 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 Sporopliore. The formation of the 

 sporangium in the Endosporece has been minutely described by 

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

 be sufficient here. The plasmodium concentrates at certain 

 points and developes into sporangia of the various forms which 

 will be found described in the account of each species; they 

 are either simple, though often densely clustered, or they are 

 combined into an cethalium, 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, 

 while in others it is subject to much variation. Two abundant 

 species, Physarum nutans and Didymium effusum, may be men- 

 tioned 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, and 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. 



* De Barv, I.e., p. 424. 



