202 



SCIEXCE-GOSSIP. 



the exceedingly fine piercing instrument, which 

 occupies a groove along its upper surface, bores a 

 passage through which the juices can be extracted. 

 Before commencing its meal, however, the Hydro- 

 metra invariably raises its prey from the water, and, 

 holding it aloft on the extremity of its rostrum, 

 enjoys it without fear of any hindrance in making 

 its escape in case of surprise by a mightier insect. 

 The piercing instrument is not barbed as in other 

 insects, but seems to be enabled to retain its hold by 

 the power of muscularly bending the tip. In lifting 

 its prey from the water the Hydrometra always 

 exerts the pull in an oblique direction, thus over- 

 coming to a large extent the attraction of the 

 water ; but, in spite of this, it appears to require 

 the exertion of all its strength to raise its burden. 



When resting it has the strange habit of lifting 

 one or both of its hind legs high in the air, in a 

 manner suggestive of the similar habit of many of 

 the gnats of extending their front pair of legs so 

 that they resemble antenna;, but which I have 

 never observed in any other insect. Possibly in 



both cases the object may be to perceive the 

 approach of enemies by the sensitiveness of these 

 delicate limbs to atmospheric motions. 



This insect undergoes very little external change 

 during its progress from the larval to the mature 

 state. There is, of course, no intermediate 

 quiescent stage, and as there is hardly a trace of 

 wings in the perfect insect, there are no rudiments 

 of these organs to indicate arrival at the state of 

 pupahood, so that this stage of existence may be 

 said to be entirely omitted. For the same reason, 

 it is a matter of some difficulty in the case of this 

 insect, as of some other apterous hemiptera, to 

 ascertain by examination of a living specimen 

 whether it is really mature or not. Perhaps the 

 best means of deciding this point is by the colour, 

 for at the last change of skin they generally, 

 although not invariably, assume a dead - black 

 appearance, whereas the immature insects are 

 always some shade of reddish-brown. 



53, Union Grant, Clapham, S.W. ; 



CHARACTERISTIC BRANCHING OF BRITISH FOREST-TREES. 



/CONTINUING my remarks 

 ^-' issue of Science-Gossip, 

 trees which have opposite leav 

 begin with Fraxinus excelsior. 

 The Ash. 

 The leaves of the ash are 

 opposite in pairs, each pair 

 standing at right angles to the 

 pairs immediately above and 

 below it. It is only in ab- 

 normal growths that there is 

 any departure from this ar- 

 rangement. It will follow, 

 therefore, as already stated, 

 that since branches originate 

 in buds, and that buds are 

 normally formed in the axils 

 of leaves, the branches will 

 stand opposite to each other 

 as did the leaves. The angle 

 at which each branch comes 

 off from the main stem, and 

 the side-branches from the 

 larger ones, is, if measured 

 above the point of junction, 

 about forty-five degrees, not 

 often less than this although 

 frequently larger. As the 



By the Rev. W. H. Perchas. 



(Continued from page 143.) 



from last month's branches increase by the growths of successive 



I take first those seasons, the augmented weight tends to bring them 



es, and of these I into a horizontal or defiexed position, but even then 



the original angle is usually preserved for a foot or 



two after leaving the main 



stem. In the younger growths 



there is a strong tendency to 



ascend, and thus the younger 



shoots make a less angle than 



forty-five degrees with their 



parent branch. 



As the branches lengthen the 

 :.-\::-\ ::' :";lis 5 e :.r:.:: ihr~ 

 downwards, but the strong 

 tendency to ascend reasserts 

 itself in each season's growth, 

 and thus the ends of the 

 branches are generally seen to 

 turn upward to a degree which 

 is characteristic of the ash. 

 The elasticity of the wood of 

 the ash, which makes it valuable 

 to the coachbuilder, allows of 

 this bending downwards more 

 than would the texture of 

 oak or elm wood. The dis- 

 tance between the succes- 

 sive pairs of leaves is in 



Ash in Winter Habit. 



