A Mouograp/t of the Myxogastres. 15 



slender stalk-like outgrowth measures from 18 — 20 ju, in length, 

 and after having become inflated at the apex and absorbing the 

 protoplasm from the parent cell, is cut off from the latter, first 

 by a septum close to the parent cell ; this is followed by the 

 formation of a second septum close to the base of the swollen 

 apical portion or spore. 



9. In the coalescence of the naked cells to form a plasmodium 

 being the result of conjugation between the component cells, 

 thus presenting features in common with the primitive forms 

 included in the group Zygosporeac. The reasons for the above 

 statement are as follows — The frequent occurrence of forms 

 intermediate between well-marked, but closely allied species, 

 suggested the idea of hybridity, especially as the supposed 

 hybrids varied in their degree of morphological agreement wdth 

 one or other of the two species between which they were 

 intermediate. With the object of ascertaining whether hybrids 

 were formed in nature, the young plasmodia of Physarum 

 leucopus and Physarum le2icophaeum were so placed that the 

 Plasmodia of the two became blended together at the point of 

 contact ; this experiment resulted in the formation of sporangia 

 intermediate between the two species from the blended portion 

 of Plasmodium, whereas sporangia typical of the two ^species 

 respectively were produced from those portions of plasmodia 

 farthest removed from the point of contact of the two plasmodia. 

 Without entering into minute specific details, it will be suf- 

 ficient to state that Physarum Icucojihacum has a dark-brown 

 stem and a thin capillitium with few knots of lime, whereas 

 Physarum leiicopus has a white stem and stout capillitium with 

 numerous large knots of lime. The hybrid has a white stem 

 and a slender capillitium with few knots of lime. In the Kew 

 herbarium there is a specimen collected at Highgate by Dr. 

 Cooke, which agrees exactly with the hybrid described above, 

 and which appears to have specially attracted the attention of 

 Mr. Arthur Lister, who in going over the collection of Myxo- 

 gastres, made a careful drawing of the specimen, adding, 

 " Pliysarum Ic acophac ion yyith a pale stalk." I have also pro- 

 duced a hybrid from two species of TricJda. Mr. Harold 



