68 H. MARSHALL WARD. 



seem to depend on the age and relative thickness of the membrane, 

 hut may be in part due to other causes. 



External to this, the proper shell of the sporangium, is a yellow net- 

 work or coarser membrane somewhat less constant in character. In 

 some cases, at any rate, it can be traced all over the surface of the 

 sporangium, but in other cases it appears to be incomplete at places. 

 The meshes of this layer vary considerably in size, and the whole net- 

 work is thicker or thinner at some spots than at others : to these 

 peculiarities may be referred the different shades of the yellow colour. 

 It is where this yellow mesh work passes off from the surface of the 

 sporangium to become extended irregularly on to the surface of the sub- 

 stratum that the yellow fringe or border (figs. 3 and 4) is observed, and 

 in a certain sense this " outer peridium," as the network might be 

 termed, may be looked upon as fixing the sporangium which it im- 

 prisons to the substratum. The relative positions of the two struc- 

 tures are no doubt due to the fact that the network is a mass of coarse 

 granular material excreted by the protoplasm of the plasmodium when 

 it is forming the spores and sporangium. 



In the large number of cases where the sporangia present the 

 typical bright black colour to the unaided eye, or when but slightly 

 magnified, this thin yellow network offers nothing further worthy of 

 note. It occasionally happens, however, that certain of the sporangia 

 referred to above as being developed not in the nutritive solution 

 but on parts of the roots which are in the damp atmosphere just 

 above the surface of the liquid, present a dull greyish appearance, in 

 place of the bright black one described in detail above : in these cases 

 the thin outer network is infiltrated with carbonate of lime in 

 varying degrees and may be closer in texture accordingly. This 

 seems to mask the yellow colour, and the network becomes a coarsely 

 granular and, it may be, brittle greyish membrane. There is much 

 variability in this connection however. 



Two points of interest present themselves here. 'First, as already 

 said, the external granular membrane or network is evidently a 

 remnant or excretion from the plasmodium, left over in the process 

 of formation of the sporangium proper from its protoplasm ; and 

 secondly, it depends on circumstances whether it contains much or 

 little calcium carbonate. My observations on the subject lead to 

 the following conclusions. 



