SCIENCE-GOSSIP. 



211 



which is the commonly-received idea of the form of 

 the leaf of this tree. 



We can conclude from this instance that the 

 warmth and dampness of midsummer in this 

 tree favours the rapid formation of the tissues, the 

 fibro-vascular bundles exceeding in length that of 

 the parenchyma in breadth ; for as the apex or 

 extremity of a leaf is formed first, which is clearly 

 decided by its withering invariably before any 

 other part, as seen in the leaves of the tobacco 

 plant [Nicotiana tabacum, Linn.) etc., the rapid 

 lengthening of the mid-rib will produce a broader 

 or narrower leaf accordingly as the parenchyma on 

 either side is formed more or less quickly. Here, 

 only a simple leaf is adduced, but precisely the 

 same thing happens in a multicostate or quinque- 

 costate leaf like that of the common fig-tree, which 

 under these circumstances would become more or 

 less divided. 



Want of light decreases the number of chlorophyll 

 corpuscules, consequently the quantity of assimilated 

 matter, and therefore the formation of parenchyma, 

 etc. ; this helps to explain the sub-division of the 

 leaves of Solamim dulcamara growing in shady 

 places, like the leaf figured on page 6i, ante (the 

 third pair of lobes are scarcely seen in the figure), 

 and also the rudimentary state of the lamina of 

 plants growing in the dark. That total submersion 

 in the case of aquatic plants tends to sub-divide or 

 narrow the leaves, is seen in Vallisneria spiralis, 

 Ceratophyllum demersmn, several Potamogetoti and 

 Utricularia, and the submerged leaves of Callitriche 

 verna, the floating rosette of the latter, which acts 

 as a peltate leaf in sustaining the weight of the 



plant, are aborate oblong and become narrower as 

 we descend on the .stem, until the ultimate leaves 

 have become linear with notched apices like those 

 of Vallisneria. 



There is no doubt that the round entire form of 

 the floating leaves of many aquatic plants are floats 

 to buoy the plant to the surface of the water, such 

 as those of several species of Nymphcea, Nuphar 

 luteum, Brasenia peltata (water-shield of North 

 America), Limnanthemum nymphceoides, Hydrocharis 

 morsus-yajtce, several LemncB, Potamogeton natans, 

 (which has sub-eliptic or ovate lanceolate floating, 

 and similar but narrower submerged leaves), 

 Nelicmhium, Ranunculus aquatilis, etc. Great variation 

 in size and form is found in the peculiar angular 

 leaves of Atriplex patula and Solanum nigrum; and 

 the leaves of the great bindweed [Convolvulus sepium) 

 vary from the normal broadly hastate form (fig. 5), 

 with angular basal lobes, to a longer and narrower 

 hastate or sub-lanceolate sub-cordate contour 

 (fig. 6) ; numerous plants with the latter form of 

 leaf I found on a shady hedge bank near Willesden, 

 There also is a great difference in the leaves of the 

 wood anemones growing in dry copses, etc., and 

 those of damper habitats ; in the former the leaves 

 are much more divided, hairy, compact, deeper 

 green and purplish, while the latter one is much 

 more delicate, with lanceolate few-toothed and 

 but little-cut segments. It is only by the 

 application of the microscope and the united 

 observations of botanists that this complicated 

 subject will be explained. 



3, Cathcart Hill, Junction Road, 

 London, N.; October, i8g6. 



STONE-CUTTING IN BORROWDALE. 



By Dr. P. Q. Keegan. 



OPEAKING generally and with strict reference 

 to microscopic technique, the volcanic rocks 

 of the Borrowdale series in the Lake District may 

 be regarded: (i) as rather soft, mostly ash and 

 slate ; (2) moderately hard ; and (3) very hard, 

 mostly lava ; though some of the altered ashes are 

 hard enough. It is with the first class that we have 

 here chiefly to deal, and for obvious reasons. If 

 we desire to obtain a fresh specimen of a rock, the 

 best plan is to collect it from a quarry ; as most of 

 the specimens, especially thin pieces, lying loose on 

 the mountain sides are more or less decomposed or 

 lichen-eaten, and will inevitably prove worthless 

 for microscopic purposes. Having selected a piece 

 of slate, or, not too tough a bit of ash, say about 

 one inch square and as thin as possible, provided 

 it is sound, the first business is to grind it flat on 

 one side. This is done by means of rasp and file. 

 I have two rasps about seven inches and five inches 



long by half-inch to three-quarter inch broad ; 

 also a series of small files, coarse and fine. The 

 dust raised in the process is considerable, but this 

 nuisance can be avoided by wetting the rock and 

 files with water, which, however, makes a mess 

 even dirtier than before. Nevertheless, we must 

 go on until one side of the rock is tolerably flat, 

 when we may relinquish the files, and proceed forth- 

 with to smooth the face so flattened. Some fine emery 

 powder must be placed on a flat piece of metal, the 

 under side of a rectangular tin tobacco-box will 

 suit, and having moistened it with water, lay the 

 flat side of the rock down and rub very hard with a 

 circular motion of the arm. This done, perform 

 the same action with the section on a piece of plate- 

 glass, using washed emery this time. Lastly, give 

 the finishing touch on a hone and a leather strop 

 dusted with putty powder. Having well washed 

 the specimen free from all particles of grinding 



