436 SECOND PART. —-MVCETOZOA. 



psittacinum, Ditm. The heaps of granules appear in this case to the naked eye as 

 small coloured patches or warts on the dry sporangium ; where there is no pigment 

 they are white. 



Didymium (Fig. 189) is distinguished by a crystalline covering of calcium 

 carbonate like hoar-frost formed of stellate glands and small single crystals on the 

 outer surface of the sporangia. The Didenna-forms mentioned above, which partly 

 approach Physarum and partly Didymium, have the wall of the sporangium differ- 

 entiated into a delicate inner layer which is free from or contains very little calcium 

 carbonate, and an outer layer, a brittle incrustation of lime, consisting of round or 

 crystalline fragments of calcium carbonate closely crowded and held together by 

 a small quantity of organic matter, which when the calcium carbonate is dissolved 

 remain behind as a delicate membrane. 



Calcium carbonate eliminated from the plasmodium in a granular or crystalline 

 form is imbedded in unusually large quantities in the basal wall of sessile sporangia 

 and in the wall of the stalk in stipitate sporangia in many of the Calcareae. In the 

 latter case a considerable amount of the salt often occurs inside the stalk and 

 columella, where it is not unfrequently associated with irregular lumps of some 

 organic substance and to a great extent fills up the cavity as in Didymium leucopus. 

 Fr. (Fig. 189) and Diachea. 



The cavity of the sporangium is either filled exclusively with the numerous spores, 

 as in Licea and Cribraria, or, as in most genera, tubes or threads of different forms 

 occur between the spores and constitute the capillitium. The capillitium of Physarum 

 and its nearest allies (Figs. 190, 191) consists of somewhat thin-walled non-septate 

 tubes which spread their branches in every direction and combine them into a net- 

 work. Many branches run from the periphery of the net-work to the wall, and are 

 firmly attached to it by their usually funnel-shaped extremities. The tubes are swollen 

 and inflated at the nodes of the net-work, forming the calcium carbonate-vesicles 

 mentioned above and sometimes also containing a pigment. All the Calcareae have a 

 capillitium which is everywhere firmly attached by the extremities of its branches to the 

 wall of the sporangium in the manner here described. In Didymium (Fig. 189), with 

 which genus Spumaria and Diachea agree in this respect, the capillitium consists of very 

 slender threads, from 1-3 to 2 \x. in breadth in D. nigripes, Fr. and D. leucopus, Fr., 

 as much as 2-4 n in D. farinaceum, which are cylindrical or slightly flattened, solid or 

 with an indication of a cavity in the form of a single line in the longitudinal axis, and 

 usually of a dirty violet-brown colour in the broader parts. The threads are usually 

 quite U'ct- from calcium carbonate ; in a few cases, as in D. physaroides, they inclose 

 single angular granules or crystals of calcium carbonate. They run in Didymium from 

 below upwards most commonly straight or sinuous in a radial direction from the 

 insertion in the stalk to the upper and lateral wall, their anastomoses usually forming 

 an acute angle. D. Serpula is remarkable for the numerous round pigment-vesi< les 

 which adhere to the threads of the capillitium, and like the spores have a violet- 

 brown membrane, but are from four to six times their size, being sometimes 

 r,o^ in diameter. 



The capillitium of the Trichiae and Arcyriae consists of tubular threads which 

 have no deposits of calcium carbonate, and are either not attached at all to the wall of 

 the sporangium or only at a few definite points. In Arcyria (Fig. 192) it is a non- 



