Roberts & Slack, on Fungoid Growths in Silica. 107 



On the 2nd April three tubular-looking threads were noticed 

 in the bottle with the cheese. Subsequent examination showed 

 them to be tubes formed by the escape of some gaseous 

 matter ; and at a later date Mr. Roberts noticed their resem- 

 blance to some appearances in a moss agate in his possession 

 (figs. 4 and 5). As the silica contracted, it formed various 

 lens-shaped bubbles, with remarkably brilliant reflecting 

 surfaces. 



On the same day a small mushroom-shaped ol)ject was 

 noticed in the bottle with the periosteum, and Mr. Berkely 

 subsequently pointed out its resemblance to Mucor clavatus. 



On the 6th April the bit of moss exhibited a conspicuous 

 groAvth of mycelium threads. This bottle, though corked, 

 slowly gelatinized. Another bottle, in which a piece of 

 parsnip was immersed in silica solution, produced a plentiful 

 growth of mycelium threads. When gelatinization had taken 

 place the cork of this bottle was removed, evaporation 

 ensued, and the silica solidified with numerous cracks and 

 fissures. The fungoid threads grew freely from the surface of 

 the silica after partial solidification had taken place, and the 

 process of cracking by slow contraction did not seem always 

 to break the slender threads. Fungoid threads growing out 

 of this partially solidified silica produced little balls of spores 

 in air. A bottle of the solution, into which a little mould 

 from stale beer was placed, was filled in a week or two with 

 fungoid growths, scattered through the silica, which gelati- 

 nized slowly. Some silica solution placed in an open evapo- 

 rating dish, slightly covered w^ith paper to keep out dust, soon 

 exhibited the fungoid threads. It M^as allowed to gelatinize 

 and solidify. It then presented the appearance of fig. 3. 



The preceding experiments show the facility with which 

 moulds will grow in a solution of pure silica in distilled 

 water, and the way in which they may be artificially fossi- 

 lized. 



It is curious to note that such delicate structures as these 

 fungoid and beaded threads are not torn or materially com- 

 pressed in the process of solidification of the colloid silica. In 

 Mr. Roberts's specimens, in which the solidification took place 

 very slowly, the fungoid plants look in as natural a condition 

 as when they were floating freely in the limpid solution. 



Mr. Roberts finds that a jelly containing 5 per cent, of 

 silicic anhydride, 10 mm. thick, will dry, after three weeks' 

 exposure to air, at a mean temperature of 10 C, or 50 F., to 

 a solid lamina 1"5 mm. thick ; but when free floating groups 

 of the fungoid fibres are compared with those artificially 

 fossilized in his specimens, there is no evidence that any 



