366 



SCJEA CE-GOSSIP. 



action of nitrogen. It seems that under certain cir- 

 cumstances nitrogen compounds can interact with 

 carbon compounds, the nitrogen drawing off the 

 oxygen from the carbon and causing a re-arrangement 

 of the elements. Thus are produced the immense 

 number and variety of organic compounds. 



In these actions nitrogen behaves as "middle- 

 man " ; i.e. all the elements pass in and out of the 

 compounds by forming a temporary union with the 

 nitrogen. Oxygen also plays an important part ; 

 indeed, so far as I can discern, nviy vital action in- 

 volves a passage of oxygen either to or from nitrogen. 



The great vital function of carbon is the storage of 

 energy. The removal of oxygen from carbon, with 

 the substitution of some other element, involves an 

 accumulation of energy in the new carbon compound. 

 Thus the complex carbon compounds in living beings 

 represent a store of potential energy which can be 

 expended in an actiA'e or kinetic form during vital 

 oxidation. 



The functions of phosphorus, sulphur, and iron are 

 very important to life, and those of several other 

 elements are only a little less important ; but they 

 cannot be discussed within the limits of this article. 



It seems probable that very diverse kinds of life 

 may occur in other parts of the universe, and that 

 different sets of elements may be engaged, according 

 to the circumstances of each case ; but the properties 

 of silicon, mentioned by Mr. Martin, do not suggest 

 vital activity; nor represent any important trade in 

 energy. We have yet to find a class of silicon com- 

 pounds which could behave like carljon compounds in 



the storing of energy. Silicon seems to perform a pas- 

 sive, not a dynamic fimction in the life of this world. 

 There are other elements whose properties seem more 

 suited than those of silicon for vital functions at high 

 temperatures : such are iodine, iron, and phos- 

 phorus. 



It is hardly probable that the surface of the earth 

 was ever at a very high temperature. According to 

 the meteoric theory, the earth began its existence as 

 a collection of cold meteoric fragments, dust, and 

 gases. Heat was produced internally by compres- 

 sion ; but the surface always retained a balance 

 between the high temperature of the interior and the 

 low temperature of stellar space. A small world like 

 ours could produce but little heat internally, and its 

 surface would always have been cooled nearly to the 

 absolute zero, had it not been for the compensating 

 action of the sun's radiation, which has kept the 

 balance at a higher level. The surface temperature 

 is shown by geological evidence to have been for 

 countless millions of years about the same as now. 

 Igneous rocks seem never to be formed at the sur- 

 face. They are produced at a considerable depth, 

 and especially at points where lateral pressure causes 

 a rise of temperature. Thus there may never have 

 been on this earth's surface a temperature high 

 enough for any kind of life but nitrogen life ; and 

 the vast age during which this kind of life h as- 

 existed helps to account for the complexity and per- 

 fection of its products. 



Kingsleigh, Colwall, Malvei-n, 

 April 10., 1900. 



ECONOMIC ENTOMOLOGY IN ARIZONA. 



By Professor T. D. A. Cockerell, F.Z.S. 



The Marked Mealy-wing. 



. C\^ October 17, 1899, at Mesa, Arizona, I found 

 on a few orange-trees in a single orchard 

 rather numerous examples of a minute flying insect, 

 a variety of Aleurodes niori of Quaintance, a species 

 of meal)'-wing. These creatures are pale lemon- 

 yellow, with four white wings, on which are rather 

 conspicuous black marks. The markings on the upper 

 wings consist of a spot on the lower margin near the 

 base, an oblique band near the middle of the wing, 

 bent sharply backwards some distance before the 

 lower margin, forming a Vi of which one arm is 

 longer than the other. A transverse band near the 

 end of the wing is broadly interrupted in the middle ; 

 and a longitudinal band passing from the tip of the 

 wing between the halves of the transverse band, or 

 sometimes not long enough to reach the latter. On 

 the under sides of the orange leaves will be found 



minute black objects, fringed with white. These are 

 the pupae of the mealy-wing, from which the adults 

 emerge. 



This is not the same mealy-wing which has been 

 so troublesome in orange groves in Florida : it may 

 readily be known from that by the markings on the 

 wings. It very closely resembles the Aleurodes mori, 

 lately described (Can. Ent., 1899, p. I) by Pro- 

 fessor Quaintance for Florida and Jamaica, infesting 

 mulberry and a variety of other trees. It has also 

 been found by Professor E. E. Bogue on leaves of 

 Moi-us rubra, growing on the grounds of the State 

 University of Ohio, at Columbus. Recognising this 

 resemblance, I sent specimens to Professor Quaintance 

 to be compared with his insect, and he replies 

 (December 17th, 1899) as follows: — " The Aleurodes 

 on orange is quite like mori, indeed. It will, how- 

 ever, average larger ; and in the adult the pattern of 

 wing-markings is somewhat different, and the red 



