AND FACTORS WHICH INFLUENCE THEM. 147 



shades of red in fair proportion. The yellows are probably attri- 

 butable to the albuminous contents of the plasm ; the reds are 

 more likely due to the cellulose substances. Both albumin and 

 cellulose are carbon compounds with hexonic bases ; and this 

 " ring-structure," as it is called in chemical symbolism, is re- 

 garded as particularly favourable to colour development. 



Purely chemical features, however, are usually obscured by 

 changing physical conditions. In the early stages of sporangial 

 formation, the plasm is still watery and reflective ; and this, in 

 conjunction with the presence of lime, albumin and cellulose, 

 or any combination of them, gives rise to light and bright tints 

 of many shades of white, yellow or red. As condensation pro- 

 ceeds, and interior structures are increasingly deposited, there is 

 less reflection of white light, the colour effects of the secretions 

 within the semi-transparent plasm become more pronounced, 

 and the tones tend to deepen or darken. By the time the 

 sporangium walls have formed, but while they are still moist, 

 there is in numerous cases an almost complete absorption of 

 light, producing a nearly black appearance. On drying off, 

 colour reappears in most instances, but with a difference. Their 

 prevailing hues are now shades of black, purple or brown ; the 

 browns, in beautiful variety, being in the ascendant. 



In the Calcarineae the general course of the coloration pro- 

 cesses is affected by the lime embedded in the walls, or masked 

 by lime-crystals encrusting the sporangia. When these fall 

 away, darker surfaces are seen. The iridescent or metallic 

 appearances presented by certain species, both of Calcarineae 

 and other genera, are due to prismatic or interference effects, 

 produced by mineral particles or surface membranes, hyaline 

 or translucent. 



Here, for the present, our analysis ends. When we are asked 

 what is the use of studying Mycetozoa, our answer is that, so 

 far as we are able, it is our business, as microscopists and nature- 

 students, " to make each small thing unfold its secret, and in 

 so doing, perhaps, to unfold other and wider secrets." 



