ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 821 



causes them to flow over the surface of the wound when the reservoir 

 is injured. 



All the substances produced by the hardening of latex and the 

 other resinous fluids in contact with the air, resin, caoutchouc, wax, 

 &c, are glutinous, and are admirably adapted for the protection and 

 healing of wounds. On escaping from their receptacle they are 

 decomposed into two parts, a thin liquid fluid, and the thick mucila- 

 ginous substance which was previously dissolved in the first. Their 

 function, in fact, appears to be identical with that of the resin and 

 terebenthin of conifers. One of the injurious results of wounds which 

 they prevent is the settlement and germination in the exposed tissue 

 of the wounded part of the spores of parasitic fungi. 



In plants and organs of the simplest structure, such as Thallo- 

 phytes, mosses, and the pi-othallia of ferns, the process of recuperation 

 after a wound is simply that the injured cells die and are not replaced, 

 the uninjured cells in contact with them carrying on the life of the 

 individual. In plants of higher organization, on the contrary, the 

 injured tissue must be replaced by a freshly formed tissue, which 

 process is carried on under the protection of these resinous secretions. 

 This new tissue is of the nature either of callus or of traumatic bark, 

 both resulting from the segmentation of cells by cell-walls parallel to 

 the surface, new layers being formed in this way, the walls of whose 

 cells are subsequently impregnated with suberous matter. 



Change of Starch into Sugar at low temperatures.* — H. Miiller- 

 Thurgau has experimented on the sweetening of potatoes by frost, 

 depending on the conversion of starch into sugar. He finds that it 

 depends on the freezing taking place slowly, and on the temperature 

 sinking to at least — '6° G. When once begun the process goes on 

 rapidly. Different kinds of potatoes exhibit very different properties 

 in this respect, and the presence of a large amount of water promotes 

 the sweetening. The transformation is occasioned by a diastatic 

 ferment, the propagation of which is promoted by a low temperature. 



Colours of Flowers.f— In an article by Grant Allen, on "The 

 Colours of Flowers, as illustrated in the British Flora," the author 

 says that the different hues assumed by petals are all, as it were, laid 

 up beforehand in the tissues of the plant, ready to be brought out at 

 a moment's notice. And all flowers, as we know, easily sport a little 

 in colour. But the question is, Do their changes tend to follow any 

 regular and definite order '? Is there any reason to believe that the 

 modification runs from any one colour towards any other ? Apparently, 

 there is. All flowers, it would seem, were in their earliest form 

 yellow ; then some of them became white ; after that, a few of them 

 grew to be red or purple ; and, finally, a comparatively small number 

 acquired various shades of lilac, mauve, violet, or blue. 



Some hints of progressive law in the direction of the colour- 

 change from yellow to blue are sometimes afforded us even by the 



* Naturforscher, xv. (1882) pp. 349-51. 



j- Allen, Grant, ' The Colours of Flowers as illustrated in the British Flora.' 

 119 pp. (Svo, London, 18S2.) Cf. Bull. Torrey Bot. Club, ix. (1882) pp. 117-8. 



