16 INTRODUCTION. 



may exhibit a Heuiitrickia-like capillitium ; and a specimen of 

 Hemitrichia fierpula from New Zealand, which has the appearance 

 of having been affected by weather at the time of development, 

 has a part of the capillitium consisting of short fusiform elaters. 

 In some extensive gatherings of Trichia affinis which have 

 matured in hot, dry weather, the elaters are so reduced in size as 

 scarcely to exceed the diameter of a spore in length, though the 

 sporangia are perfectly normal in form, and the spores are marked 

 with the typical sculpture. In fitemonitis, Lamproderma, Proto- 

 tricliia, and other genera, great variations are caused by changes 

 of temperature ; but in none of these cases which have come under 

 my observation is there any indication of a transition from one 

 species to another. An interesting account is given by Dr. Rex 

 of a remarkable and abnormal development of tStemonitis splendens, 

 referred to under the description of that species in this work, 

 where, through successive generations, a gradual return took 

 place to the normal type. In this instance other causes than 

 change of temperature must have taken part. 



Although the search for specimens of the Mycetozoa has 

 been comparatively limited, owing, no doubt, to the small size 

 of the objects, yet in consequeDce of the persistent nature of 

 the sporangia, we possess, in the different herbaria, specimens 

 representing the gatherings from many countries during more 

 than half a century, and some of them dating back to nearly 

 a hundred years. Where they have escaped rough treatment, 

 they completely retain their specific characters. In reviewing 

 these specimens one is struck with the completeness of the 

 group and the general stability of the species ; and when we 

 consider their cosmopolitan distribution, owing, we may conclude, 

 to the long- continued vitality and minuteness of the spores, it 

 may be doubted whether any hitherto unsearched region will add 

 very largely to the number of species with which we are already 

 acquainted. It is their life history which is at present imperfectly 

 known, and it is in this direction that the important work of the 

 future must lie. 



The affinities of the Mycetozoa have been dealt with by de Bary 

 and Zopf in the works before referred to. 



It had been suggested that they were allied to the fungi 

 through the Chytridece, which do not always form a myce- 

 lium, and in which the entire vegetative body is finally trans- 

 formed into a many-sporecl sporangium, the vegetative body 

 and spores having the power of amoaboid movement for a longer 

 or shorter time. De Bary, however, mentions among other 

 points of difference that the Chytridece do not form a plas- 

 modium by the coalescence of swarm-cells, " and there is there- 

 fore no ground for assuming their direct relationship with the 

 Mycetozoa."* 



The position of the Acrasiece in which the swarm-cells exhibit 



* De Bary, I.e. , p. 445. 



