436 SECOND PART,—MYCETOZOA. 
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 Diderma-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 capzllitium. 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 in breadth in D. nigripes, Fr. and D. leucopus, Fr., 
as much as 2-4 » 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 free 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-vesicles 
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 
50p 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- 
