2IO 



SCIENCE-GOSSIP. 



VARIATIONS OF THE LEAF-BLADE. 



Bv H. E. Griset. 



'npO the botanist the important subject of the 

 variation of the lamina, and the cause of 

 this variation, will ever possess the highest 

 interest, from its value in the determination of 

 plants ; and there is little doubt that warmth and 

 moisture in the case of terrestrial plants favour 

 the growth of the parenchymatous and vascular 

 tissues, as Mr. J. A. Wheldon remarks in his notes 

 in the October number, upon the article of the 

 above heading. What can be the use of the dense 



one whole season ; it will generally be found that 

 the leaves become larger as the warm weather 

 advances. Thus on a single shoot about nine 

 inches long, on May ist, a leaf was mature, it 

 was simply three- lobed, the casta of the median 

 lobe being lo centimetres long (lo centimetres, or 

 I decimetre = 3'937o8 inches), (fig. ij (-). On 

 June 2nd, four more leaves had been formed, 

 the fifth being deeply five-lobed with a median 

 costal length of 15 centimetres (fig. 2) ; and on 



R^ 1 



Variations of the Leaf-blade. 

 Figs. 1-4, leaves of the fig-tree, Ficus carica ; figs. 5, 6, leaves cf the great bindweed. Convolvulus sepiiim. 



epidermis and mostly entire or solid form of the 

 leaves of many succulent plants ? Is it not to 

 protect the more delicate parenchyma, w-hich in 

 membranous and divided leaves would obviously be 

 rapidly deprived of moisture in the dry atmosphere 

 of the habitats of these plants ? 



In studying the forms of the leaves of the same 

 species we are generally led to the conclusion that 

 the largest and most divided leaves are produced in 

 the most favourable time of the year, which, of 

 course, varies with the species. This is well illus- 

 trated : if the minute differences in the leaves of 

 the fig-tree (i) (Ficus carica) are carefully noted for 

 (') This tree, which grew on a garden wall facing the west, 



June -iSth, three more leaves were matured, the 

 eighth being seven-lobed, with a median costa of 

 168 centimetres (fig. 3). Of course the other leaves 

 formed the gradations between those cited to show 

 the striking difference in size and division ; the 

 shoot had, in the meanwhile, lengthened to sixteen 

 inches on eight additional nodes. In the autumn, 

 the newlj'-formed leaves again become smaller, 

 stouter, five-lobed and less divided, as seen in the 

 typical form at this period, represented at fig. 4, 



produced a shoot on the trunk which grew thirty-three inches 

 in twenty-two days {from June loth to July 2nd), which is a 

 daily average growth of i"5 inches. 



i-i All my drawings are from the actual objects and correct 

 to scale. 



