THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



SUPPLEMENT TO VOL. LX. SEPTEMBER 1842. 



LV. — The Physical Agents of Temperature, Humidity, Light, 

 and Soil, considered as develojnng Climate, and in connexion 

 with Geographic Botany. By Richard Brixsley Hinds, 

 Esq., Surgeon R.N. 



[Concluded from p. 475,] 



I HAVE frequently had an opportunity of observing that 

 plants produce two kinds of mould, with what has appeared 

 to me sufficient distinctive characters to justify a separation. 

 It is in humid atmospheres that growth and decay take place 

 with such rapidity, and here is the proper field for studying 

 the unobtrusive deeds of the vegetable kingdom. The first 

 kind is formed around the surface of attachment of plants, 

 and indifferently whether they are fixed to rocks or the trunks 

 of trees. On separating Algae from rocks, or removing an 

 investment of mosses from the surface of forest trees, a thin 

 layer of mould of a dingy yellow colour is exposed ; but it is 

 always very sparingly produced. The origin may be from se- 

 veral sources ; in some cases from the partial disintegration of 

 the supporting rock, but in all probability the greater part is 

 derived from matter excreted from the plants themselves, in- 

 creased by foreign substances getting entangled among the 

 leaves and fronds. This is the kind produced on those sur- 

 faces recently occupied by a few plants for the first time. The 

 second variety results from dead vegetable matter ; it has its 

 origin in the decomposition occurring in the solid parts of ve- 

 getables, as the trunks of trees, their bi'anches and the stems 

 of shrubs. A beautiful deep black rich mould is produced, 

 when rubbed between the fingers feeling like an impalpable 

 powder, and consisting entirely of soluble matter capable of 

 administering to the nutrition of future plants. After trees 

 fall from their ranks in the forest the destructive agents are 

 soon at work, and the huge trunks become converted into 

 this black mould. Their external appearance often does not 

 indicate the state within ; and it is only when a stray footstep, 

 or some other external violence, breaks through the thin crust 

 of bark, that the metamorphosis becomes evident. 



Still I am not prepared to admit, that lichens and mosses 

 Ann. ^ Mag. N. Hist. Vol. ix. Si/ppl. 2 M 



