AN AQUATIC MYXOMYCBTE. 67 



slug or planarian : it varies in diameter from | a millimeter to 1| 

 millimeters or more, and stands up from the epidermis of the root, to 

 which it is attached by a slightly flattened base. As shown both by 

 sections and by the ease with which the sporangium can be detached 

 from the root by means of a razor or even the point of a needle, the 

 sporangium is only fixed on to the outside of the epidermal layer, or 

 to the outer cells of the root-cap, and is in no way connected anatomi- 

 cally with the interior of the cells or tissues : in some cases, however, 

 it can be shown that the base of the sporangium is actually in contact 

 with the external cell-walls of the root, and not merely adherent to 

 the slime, &c, found on the surface. 



When detached, examination fails to show any aperture in the 

 sporangium, or any special organs of adhesion, except in so far as the 

 thin network to be referred to shortly, and which passes off from the 

 surface of the sporangium to that of the root may be looked upon as 

 a hold-fast. 



On slightly magnifying the sporangium (figs. 2, 3, and 4) it is at 

 once noticed that the smooth hard black appearance is due chiefly to 

 two causes. In the first place the thin outer covering or shell reflects 

 the light in various ways from its rounded surfaces, which are, more- 

 over, wet and bright, and evidently coloured with a dark pigment ; 

 and secondly the densely packed, minute, purplish-brown spores in 

 the interior render the whole mass perfectly opaque, except at the 

 edges where they may be seen shining through with more or less dis- 

 tinctness (figs. 3 and 4). 



Closer examination now shows also that the deep black mass of 

 sporangium and contents proper is fringed as it were (at any rate in 

 most cases) with a bright canary yellow border, and, as will be shown 

 below, this extends over the sporangium proper as a sort of outer coat 

 or network. 



The whole sporangium, then, is composed of two coats — an inner coat 

 composing the wall of the sporangium proper, is a thin, tough, very 

 elastic and almost horny homogeneous membrane, which is quite 

 smooth or nearly so, being occasionally marked with almost irnpercep* 

 tible rugosities. Its colour is, as already stated, dark, and evidently 

 due to a purple-brown pigment usually evenly distributed throughout 

 its substance. In comparatively rare cases the pigment is nearly absent 

 in places, and the depth of its hue varies somewhat ; these variations 



