OSMOTIC GHOWTII 



137 



Capsules or closed shells may be produced in the same way 



by superimposing a layer of somewhat greater concentration. 



These capsules consist of two valves joined together at their 



circumference. The lower valve is thick and strong, while the 

 valve may be transparent, translucent, or opaque, but is 



aiways thinner and more fragile than the lower one. 



Ferrous sulphate sown in a silicate solution gives rise to 



growths which are green 



in colour, climbing, or 



herbaceous, twining in 



spirals round the larger 



and more solid calcareous 



growths. 



With salts of man- 

 ganese, the chloride, 

 ■•hate or sulphate, the 



stages of evolution of the 



•"'■owlh are distinguished 

 only by diversities of 



torn , DO . by modifi- 



cations of colour. We 



may thus obtain terminal 



orgatas black or golden 

 yellow in colour on a white 



stalk. In a similar way 

 we may obtain fungi with 



,1 white stalk and a yellow 

 cap. of which the lower 

 surface is black. 



Very beautiful growths may be obtained by sowing calcium 

 hloridc in a solution of potassium carbonate, with the addition 

 of 2 per cent, of a saturated solution of tribasie potassium 

 phosphate. This will give capsules with figured belts, vertical 

 lines at regular intervals, or transverse stripes composed of 

 projecting dots such as may be seen in many sea-urchins. 

 These capsules are closed at the summit by a cap. forming an 

 operculum, so that they sometimes appear as if formed of two 

 valves. Now and again we may see the upper valve raised by 



Fig. 49. 



-Osmolic capsular growth with 

 figured belt. 



