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The Kight Sign for February. 



ZODIACAL MAPS. 



THE Nigbt Sign for February should have been given 

 last month. It originally appeared in our issue for 

 February 1, 18S4, but then contained the paths of Mars 

 and Jupiter. We now repeat it, and shall in a fortnight's 

 time repeat the Night Sign for March, in order to complete 

 the series of twenty-four Zodiacal Maps. 



FORMS OF LEAVES. 



A LECTUBE 



By Sia John Lubbock, Babt., M.P., D.C.L., LL.D., 

 F.RS., &c. 



(Continued {rom p. 174.) 



XT TE have hitherto been considering mainly deciduous 

 VV trees. In evergreens the conditions are in many 

 respects different. It is generally said that leaves droj) off 

 in the autumn because they die. This, however, is not 

 strictly correct. The fall of the leaf Ls a vital process, con- 

 nected with a change in the cellular tissue at the base of 

 the leaf-stalk. If the leaves are killed too soon they do 

 not drop off. Sir John illustrated this by some twigs 

 which he had purposely broken in the summer : below the 

 fracture the leaves had been thrown off; above, they still 

 adhered, and so tightly that they could support a con- 

 siderable weight. In evergreen trees the conditions are, in 

 many respects, very different. It is generally supposed 



that the leaves last one complete ycir. Many of them, 

 however, attain a much greater age ; for instance, in the 

 Scotch fir, three or four years ; in the spruce and silver, six 

 or seven ; in the yew, even longer. It follows from this 

 that they require a tougher and more healthy texture. 

 When we have an early fall of snow, our deciduous trees 

 are often much broken down ; glossy leaves have a 

 tendency to throw it off, and thus escape, hence 

 evergreen leaves are very generally smooth and 

 glossy. Again, evergreen leaves often have special 

 protection, either in an astringent or aromatic taste, which 

 renders them more or less inedible ; or by thorns and 

 spines. Of this the holly is a familiar illustration, and it 

 was pointed out that in old plant.s, above the range of 

 browsing quadrupeds, the leaves tend to lose their spines 

 and become unarmed. The hairs on leaves are another form 

 of protection ; on herbs the presence of hairs is often asso- 

 ciated with that of honey, as they protect the plants from 

 the visits of creeping insects. Hence, ])erhaps, the ten- 

 dency of water f<pecies to become glabrous, Pohj(jonum 

 ampliihiuin being a very interesting case, since it is hairy 

 when growing on land, and smooth when in water. Sir 

 John then dealt with cases in which one species mimics 

 another, and exhibited a sti iking photograph of a group of 

 stinging nettles anil dead nettles, which were so much alike 

 as to Vje hardly distinguishable. No one can doubt that the 

 stinging-nettle is protected by its poisonous hairs, and it is 

 equally clear that the innocuous dead nettle must profit by 

 its similarity to its dangerous neighbour. Other similar 

 cases were cited. 



