HARDWICKE'S SCIENCE-GOSSIP. 



57 



generally the fullest-grown : the males are active, 

 and are very small. There are many species of the 

 same insect, known as C. Vitls, C. Testudo, C. Hes- 

 peridum, &c. They should be exterminated as soon 

 as they appear, for if let get ahead, there will be 

 great difficulty in effecting this afterwards, as they 

 increase at a prodigious rate. Another pest is the 

 " Mealy Bug " (fig. 23). This is not unlike the 

 common Wood-louse, but is of a reddish colour, 



Fig. 29. Fu'l- grown Thrip, x 25. 



and covered with a white mealy powder. The male 

 is slender, shaped somewhat like a gnat, has a pair 

 of broad wings, and two brush-like appendages 

 behind. The last member of this craft that 1 shall 



Fig-. 31. Upper side of 

 Scale Insect, x 20.3 



Fig. 30. Larva of Thrip, x 25. ^S- 32 Under side of 



ditto, x 25. 



allude to is Acarus tellarius (fig. 27), better known as 

 the " Red Spider " ; in fact, although last named, 

 it is not least in its power of destruction, and the 

 difficulty of eradication: being excessively small, it is 

 not easily seen unless by keen eyes. It is generally 

 of a bright brick-red, yellow or brown colour ; on 

 ea-h side of its back is a small black spot: this only 

 is seen when magnified. Its shape is similar to the 



generality of the Acari tribe. It is found on the 

 underside of the leaves of the plant infected; while 

 there it sucks the juices out of them, and by the 

 web it spins from vein to vein, destroys the power 

 of healthy inhalation of the life-giving gas; the 

 leaves then turn of a pale colour and fall off. This 

 in many instances destroys the vitality of the plant. 

 One thing is very remarkable, — how Nature has 

 provided for the safety of these insects by giving 

 them the instinct to hide from general view, on the 

 underside of the leaves, telliug them, as it were, 

 "that they are thieves, and must work in the dark." 

 There are many modes for destroying these enemies 

 of vegetable life, the principal being fumigation, 

 syringing, and painting the stems and leaves with 

 compounds of a powerful nature. Deeming it 

 would be unsuitable in this paper to give a recipe 

 for each application, they in fact being " legion," 

 I shall conclude by saying that these are to be 

 found in most horticultural works, which are easily 

 attainable for reference. 



Ralph H. Westkopp, B.A., T.C.D. 

 Attyjl'ui Park. 



DEFOLIATION, AND SIMILAR VEGETABLE 

 PHENOMENA. 



OE all the theories which, intended to account 

 for such phenomena as defoliation, defloration, 

 &c, none of them to my mind can be regarded as 

 satisfactory when viewed in the light of certain well- 

 established facts connected with botanical teaching 

 generally. 



The conclusion I have arrived at, is one which 

 being obviously justified on natural, physiological, 

 and scientific grounds, I accept as the most probable 

 and supportable theoretic explanation, as perhaps it 

 is possible to give in accounting therefor. 



In the first place we will, in order to comprehend 

 the matter aright, take the conditions necessary to 

 the formation of the green colouring principle of 

 plants, — Chlorophyl. That this must have for its 

 development light, is indisputable ; also that it is 

 dependent upon the sap as its distributing medium, 

 is alike incontestable ; and then connected with the 

 sap, which I take to be analogous to what blood is 

 in animals, there is another, and that an all-important 

 point, to be recognized in considering the subject, — 

 it is Cold. Now from observation we all know, and 

 that all the better because reminded of it every year, 

 the effects that cold winds, frosts, &c, have upon 

 leaves and other temporary organs of plants, such 

 as the flower and fruit. Still in none of them do we 

 notice it so much as in the leaves. Eor these, so 

 soon as autumn commences, begin, as a rule, to 

 wither and assume their autumnal tint, and even- 

 tually to defoliate. But in this, as inmost other 

 things, we have exceptions. Else, what of the ever- 



