INTRODUCTION. 1 5 



swarin-cells show that C&ratiomyxa belongs in essential points to 

 the Mycetozoa, but with modifications in the intermediate stages 

 of development. 



As has been stated before, many species of the Nycetozoa are 

 associated with numerous varieties, using the word species as a 

 name given for the convenience of classification to a form 

 possessing definite and permanent characters which distinctly 

 separate it from any other ; and the word variety to such as are 

 linked with the type by a close series of connecting forms, and 

 although more or less stable, do not possess such distinctive 

 characters as would render it expedient or helpful to mark them 

 with specific rank. 



The geographical distribution of most of the species is very 

 wide, and the main characters are remarkably constant in 

 specimens gathered in all parts of the world. 



Specimens of Heinitrichia clavata, II. Serpula, Dictydium umbi- 

 licatum, and Trichia fall ax, obtained from Europe, India, and 

 North and South America, are identical to the most minute micro- 

 scopic detail ; and numerous other equally stable forms might be 

 cited. On the other hand, the American and tropical species of the 

 genus Cribraria are more elegant in form than individuals of the 

 same species here and on the Continent, and most of them show a 

 tendency, in the great regularity of their structure, towards the 

 type of C. intricate^ a striking and well-marked species which is 

 abundant in those regions, but rare in our less brilliant atmo- 

 sphere. The genus is largely represented in America, and inter- 

 mediate forms between the recognised species are frequent ; some 

 of these are described by Dr. Rex in letters to me as being 

 constant in gatherings from several States, but they are so 

 closely allied to established types that he hesitates to give 

 them separate specific names. The more elegant growth in the 

 American species is not confined to the genus Cribraria, but 

 is of general occurrence ; and it is probable that the slight 

 modification of the prevailing type is due to the influence of 

 climate. This is what might be looked for when we consider 

 the effects which changes of weather produce in the develop- 

 ment of sporangia in. this country. On old decaying stumps 

 which can be kept under observation for several years, we may 

 have growths of Trichia affinis, which year after year present 

 the same typical characters, only differing in the elaters 

 in one season being slightly thicker than those in another. 

 When cold weather sets in while the plasmodium is rising, the 

 arrangement of the spiral bands is so abnormal as to suggest a 

 marked variety, but with a return of milder weather the original 

 form reappears, leaving no doubt that all have been derived from 

 a common parentage. Developments of Trichia j^Grsimilis of the 

 typical form have been followed after a few nights' frost by a 

 growth in which the short and nearly smooth elaters clos ly 

 resemble those of Oligonema nitens, though the spores and the 

 shape of the sporangia retain the normal character. T. scabra 



