Maech 1, 18G5.] 



SCIENCE. GOSSIP. 



55 



of progression or development all throughout 

 nature, and beautifully marked upon a bri\nch 

 of Araucaria, or the cone of a fir. The volute 

 may be greater or it may be less, and the in- 

 vestigations of Braun and Henslow have 

 reduced the spiral regulation of leaves to 

 mathematical precision. It; is well known 

 that the leaf upon the stem or branch origi- 

 nates in a node, the leaves being " altex-nate " 

 when each node produces a single leaf on 

 different sides in succession ; and " opposite " 

 when tv/o leaves originate in anode and stand 

 out face to face. Two spirals are in the latter 

 case to be considered as passing up the stem ; 

 and in the case of three or more leaves from 

 the same node forming a whorl, the spiral is 

 held to be reduced to a circle. The stems of 

 twining-plants, like honeysuckle and convol- 

 vulus, evince the disposition of the entire 

 structure to take the spiral twist. The 

 leaves of banana exhibit the same ten- 

 dency, in common with the leaves of many 

 plants while in the bud, and in common also 

 with tendrils and similar modifications of 

 leaves which follow the same law, and even 

 with the flower-stalk in Cyclamen, and the 

 seed-vessel in Streptocarpus. In the ripe 

 strawberry the numerous small pistils, erro- 

 neously termed seeds, dotted over its surface 

 follow the spiral arrangement ; for as the soft 

 juicy part of the strav/berry is only an en- 

 larged foot-stalk, the numerous minute pistils 

 or seed-vessels Vvdiich it bears are arranged 

 accordinof to the law which regulates the 



o ... 



position of leaves. The peas in the interior 

 of a pod alternate with each other on the 

 opposite sides on the true spiral arrangement, 

 and even the seeds in the seed-vessel of the 

 wallflower, though fivr more numerous ; nay, 

 those in the common foxglove (Digitalis), 

 which are more abundant still. 



The leaf of every tree possesses individuality. 

 Its aggregate of leaves make up the character 

 by which the tree is known. No doubt the 

 tree possesses also what arboriculturists term 

 its own " habit," and by that in some measure 

 it is known and recognised. Nevertheless, 

 the leaf is its characteristic element and em- 

 blem, and in all probability imparts the habit 

 in question. In the following figures we 

 have the cherry leaf and theleavesof the beech, 

 the lime, and the poplar (figs. 7, 8, 9, 10) ; — 

 And it has been ascertained from minute 

 comparisons that the leaf is to a great extent 

 a model of the tree. For instance, the beech 

 leaf, it will be seen (fig. 7), has little or no 

 leaf-stalk ; now, the beech tree in its growth 

 is naturally feathered, from its base, with 

 branches. Accordingly the leaves of the 



beech, the oak, the elm, the box, the hollj, 

 the laurel, the bay, arbutus, laurustinus, 

 privet, and suowberry, whose natural tendency 

 is to cover ^he ground from, the base, have 



Fig. 7, Beech. 



either a very short petiole or none at all. 

 The beech leaf, too, like its branches, will be 

 observed to throw out a venation nearly pa- 

 rallel—the angle being from 45° to 50° whilst 



CiiERur. 



the midrib is rather inclined to zigzag. The 

 cherry leaf (fig. 8), and the leaves of the lime 

 and ])oplar (figs. 9 and 10), are endowed v/itli 

 leaf-stalks, and represent trees with a bare 

 trunk, as do the leaves of the apple, the pear, 

 the birch, the chesnnt, and sycamore. The 

 lime leaf (fig. 9) aflfords an illustration of the 



