SCIENCE-GOSSIP. 



361 



size sufficient to show all the necessary details. 

 As, however, I think the eye can convey the idea 

 of size by drawings better than the mind can 

 grasp by the thought of millimetres, the differ- 

 ences in the sizes of the British mites of the 

 genus Curvvpes known to me are shown by a series 

 of ovals represented by figs. 39-48. These will, I 

 think, convey the impression intended. I have 

 endeavoured to give the average size of all the 

 mites in the text by measuring several specimens 

 of the same species, adding the sizes all together 

 and dividing by the number of mites measured. 

 In several cases my measurements do not agree 

 with Piersig's ; but this may.be only due to local 



©f u-j U/j (y) 



Relative Sizes of Species or Cttrvipes. 

 Fig. 39.— C. nodatus. Fig. 40— C. longipalpis. Fig. 41.— 

 C. uncatus. Fig. 42.— C. fuscntm. Fig. 43.— C. rufus. 

 Fig. 44.— C. conglobatus. Fig. 45.— C. ohturbans. Fig. 46.— 

 C. carneus. Fig. 47.— C. longicornis. Fig. 48.— C. circularis. 



differences. All Piersig's measurements are based 

 on water-mites found in Germany, whereas mine 

 are from mites found in Great Britain. 



If any collector of water-mites has been fortunate 

 enough to find in this country other species of the 

 genus Curvipes than those I have recorded, it is to 

 be hoped that a note of its occurrence will be sent 

 to Science-Gossip. Doubtless several more are 

 yet to be discovered, as the list of British species 

 is far less in number than those of the German 

 fauna. This discrepancy is probably due to the 

 paucity of students of water-mites in these islands, 

 and the fact that much of the freshwater has con- 

 sequently not yet been searched. 

 20, Cortayne Road, 



Hurlingham, London, S.W. 



INDIARUJBBEE. 



By A. B. Stall. 



TI^HE ever-increasing demand for indiarubber is 

 J- stimulating collectors to find an adequate 

 and permanent supply, and the most likely parts 

 of Africa are at present being searched for fresh 

 sources. The demand has risen in this country 

 from 23 tons in 1830 to nearly 20,000 tons last 

 year, with a value of ,£4,000,000. Other countries 

 import considerable quantities, but all of them 

 are far behind this amount. The rapid growth 

 and enormous expansion of a trade which may 

 yet be said to be only in its infancy is remarkable. 

 The purposes for which rubber is now xised are 

 innumerable; tyres for the cycling trade alone 

 demand an enormous supply, and there is scarcely 

 an art or manufacture nowadays in which it does 

 not play an important part. 



The species of plants which yield the milky 

 juice from which the substance called caoutchouc, 

 better known as indiarubber, is obtained are 

 numerous, and distributed over almost every part 

 of the tropical regions ; yet they seem to be con- 

 fined to the spurge, nettle, and dogbane families. 

 The production of rubber in its wild state is 

 rapidly diminishing, and this is due somewhat to 

 the destructive methods the natives use in 

 extracting the juice. There are several systems 

 of preparing the rubber, the essential part con- 

 sisting in separating the water, of which there is 

 a large quantity, from the milky juice. This is 

 done either by evaporation by means of a heating 

 arrangement, or obtaining the coagulation of the 

 rubber by certain chemical processes. Rubber pro- 

 duced in the latter way is not so good. A French 

 writer says : — " Le procede est ingenieux, mais les 

 resultats de son application sont mauvais/' A 

 mechanical method for extracting the rubber on the 

 same principle as the cream separator has lately 

 been invented, and is likely to prove of consider- 

 able value. 



The cultivation of rubber-yielding plants is now 

 attracting attention, and to Great Britain this is 

 a matter of special importance, for it is to this 

 country that nearly one-half of all the rubber col- 

 lected is sent. The prospects of obtaining larger 

 supplies in the future from cultivated trees are 

 fairly promising, and in selecting sites for planta- 

 tions preference is being given to localities where 

 the trees are already growing. It is found that 

 where rubber trees are cultivated under suitable 

 conditions, they will yield a larger quantity of;milk 

 than wild trees, and the rubber, from the greater 

 care and attention paid to it, is more uniform in 

 quality, and consequently obtains a higher price. 



Para rubber produced from Hevea brasiliensis, 

 one of the spurgewort family, is the most valuable 

 of all the rubber trees, its price practically ruling 

 the market. Its home is in Para, a vast region in 



