INTRODUCTORY 3 



duced to spread over a plate of moist glass, and so be transferred to 

 the stage of a microscope, there to exhibit in the richest and most 

 interesting and abundant fashion the streaming protoplasmic cur- 

 rents. As just indicated, the plasmodia follow moisture, creep from 

 one moist substance to another, especially follow nutritive substrata. 

 They seem also to secure in some way exclusive possession. I have 

 never seen them interfered with by hyphae or enemies of any sort, 

 nor do they seem to interfere with one another. Plasmodia of two 

 common species, Hemitrichia clavata and H. vesparium are often 

 side by side on the same substratum, but do not mix, and their per- 

 fected fruits presently stand erect side by side, each with its own 

 characteristics, entirely unaffected by the presence of the other. On 

 the other hand, it is probable that some of the forms which, judged 

 by their different fructifications, and by this alone, are to us distinct, 

 may be more closely related than we suspect, and puzzling phases 

 which show the distinctive marks supposed to characterize different 

 species are no doubt sometimes to be explained on the theory of 

 Plasmodia! crossing; they are hybrids. 



Under certain conditions, low temperature, lack of moisture, the 

 Plasmodium may pass into a resting phase, when it masses itself in 

 heaps and may become quite dry in lumps of considerable size, and so 

 await the return of favorable conditions when former activity is 

 quickly resumed. Sometimes the larger plasmodia pass into the rest- 

 ing phase by undergoing a very peculiar change of structure. In 

 ordinary circumstances the abundant free nuclei demonstrable in the 

 Plasmodium afford the only evidence of cellular organization. In 

 passing now into the condition of rest, the whole protoplasmic mass 

 separates simultaneously into numerous definite polyhedral or paren- 

 chymatous cells, each with a well-developed cellulose wall.^ When 

 the conditions essential to activity are restored, the walls disappear, 

 the cellulose is resorbed, and the Plasmodium resumes its usual habit 

 and structure. 



The plasmodial phase of the slime-mould, like the hyphal phase of 

 the fungus, may continue a long time ; for months, possibly for years. 

 The reason for making the latter statement will presently appear. 



1 DeBary, Morphology and Biology of the Fungi, p. 428. 



