August 2, 1897.] 



KNOWLEDGE. 



197 



fully out ; at the same time the little crumpled wings are 

 drawn out of their eases, then the legs one by one, the 

 imago now hanging with head bent right back and the 

 wings pointing upwards, the whole insect hanging, with 

 six segments of the abdomen exposed, wet and limp from 

 the dry nymph skin, still clinging firmly to its support by 

 its stiff and empty legs. (See Figs. 3, 4, and 5.) 



After hanging like this for some ten minutes or more, 

 until the legs are strong enough, the insect, by a quick 

 contraction of the body, suddenly lifts its head, and 

 seizing with all six legs the dry nymph skin, quickly 

 withdraws the remaining four segments of the abdomen 

 out of its sheath, and hangs by its legs alone (Fig. 6), 

 The wings now hang down and begin slowly to expand, 

 at first dull and mealy-looking ; as they lengthen they 

 get flatter and clearer, until in about half an hour they 

 show all the beauty of their gauzy texture. They are 



THE MINISTRY OF LEAVES. 



By Rev. Alex. S. Wilson, M.A., B.Sc. 



THE colours of the two great kingdoms of organic 

 nature present a striking contrast ; as a whole the 

 colours of animals are characterized by variety, 

 those of plants by uniformity. Blossoms, indeed, 

 vie with insects and birds in the brilliancy and 

 diversity of their tints, but the higher plants alone bear 

 coloured blossoms, and these are few in comparison with 

 the leaves. Although leaves present every diversity of 

 shape, they are, for the most part, of one colour, and this 

 uniformity is determined by the function they perform in 

 the economy of nature. 



Foliage owes its greenness, as is well known, to the 

 presence in the cellules of the leaf of a colouring matter 

 called chlorophyll, occurring in the form of little rounded 



Fig. 6. 



Fig. 7. 



Fia. 8. 



The Dragon Fly emerged and hanging on the Nymph Skin ; the Body stiffens and darkens, and the Wings slowly expand. 



Photographed from Life. 



stm, however, very pale green and soft, and the body 

 of the insect is still wet and limp ; but as the fluid 

 which fills the animal is exuded drop by drop, the body 

 stiffens and darkens, the wings dry, and are raised and 

 then lowered to the position so well known. After about 

 five hours from first emerging from the water, the perfect 

 dragon fly is ready with quivering wings for its new life, 

 often, alas ! to be cut short within an hour by a hungry bird. 

 It may seem incredible that birds should be able to catch 

 so rapid a flier, but when first out the dragon fly is not 

 so very rapid on the wing, and is, when fluttering or resting, 

 a most conspicuous object. The poor ethereal demoiseUe, 

 almost before she has tasted the joys of her new and 

 beautiful life, is snapped up by a vulgar sparrow. 



The figures are life size, some of the emerging imago a 

 trifle enlarged ; they are taken from living specimens 

 except Fig. 1, it being impossible to photograph the 

 extended mask from life. 



of 



particles. In the Ufe of plants chlorophyll plays a role 

 highest importance. 



The action of plants on the atmosphere was first con- 

 vincingly proved by Dr. Priestley, the discoverer of oxygen. 

 He placed a mouse in an air-tight glass jar, and, of course, 

 found that after a time the mouse died, having exhausted 

 the air contained in the jar. By repeated trials he ascer- 

 tained how long the quantity of air which the jar held 

 was capable of supporting the respiration of a mouse. 

 The jar was then charged with fresh air ; a living mouse, 

 together with a growing plant, were introduced into it, and 

 the whole exposed to sunlight. In this instance the mouse 

 did not die when the usual time had elapsed, but continued 

 to live as long as Dr. Priestley cared to prolong the 

 experiment. In this way he satisfied himself that plants 

 possess the power of regenerating vitiated air which has 

 become unfit for animals to breathe, owing to the prepon- 

 derance of carbonic acid. 



