34 



SCIENTIFIC NEWS. 



[July 13, 1 J 



the warmth of spring causes the sap to rise till the 

 plant is gorged by it, and the protoplasm to resume its 

 activity, the whole apparatus of vegetation being again 

 set in motion. The embryonic tissue at the growing 

 point and at the apices of the younger leaves now begins 

 to divide, whilst those cells which have ceased to divide 

 become watery and enter upon the period of elongation 

 by which they receive their outward form and size and 

 which causes that rapidity of growth which is so striking. 

 The older parts commence to undergo that internal 

 differentiation which results in certain alterations in the 

 cell-walls and other partly formed structures — pittings, 

 lignification, etc., and the formation of stomates in the 

 epidermis — that complete growth. Then it is that the 

 leaves rapidly expand, reversing as they do so the order 

 of growth followed when forming in the bud when they 

 curved upwards and inwards closely enveloping the axis, 

 whilst now they curve downwards and outwards. This 

 diversity is due to a curious property of plants known as 

 Bilaterality which under certain conditions plays a very 

 important part in their life-history and displays itself in 

 an unequal growth of the sides of different structures, as 

 in the leaves of the bud which when first forming grew 

 more rapidly on their outer and under sides (Jiyponasty), 

 ■ the tension on the opposite side causing them to bend 

 upwards, whilst in expanding they grow more rapidly on 

 their upper and inner sides (epinasty), causing them to 

 bend outwards and downwards. The mode in which 

 they are arranged or packed in the bud is interesting, and 

 varies greatly with the species, and is termed vernation. 

 If a leaf-bud of any kind — the larger the better — be cut 

 transversely and examined carefully with a hand-lens, 

 each individual leaf will be seen to be folded in a certain 

 way upon itself and also placed in a certain position with 

 regard to the leaves nearest it. In the single leaf the 

 vernation varies from the simple inflc.xcd (fig. 5, a, b), or 

 folding of the upper half of the leaf upon the lower (Tulip- 

 tree), to the more complex convolute (fig. 5 e), or rolling of 

 the leaf laterally from one margin to the other, as 

 one would roll paper (apricot and banana), and in 

 the relative position of one leaf to another from the 

 valvate (fig. 6 a), where the leaf-margins merely touch, 

 to the supervolute (fig. 6 g), where one convolute leaf 

 is rolled round another (apricot). A most beautiful form 

 of vernation of individual leaves is the circinnatefhg. 5 d), 

 as seen in the tender coils of the fern. The examination of a 

 series of buds would with a little care and patience be a 

 pleasing exercise, and one calculated to increase know- 

 ledge of vegetable form. The folding of the sepals and 

 the petals in flower-buds, known as astivation, is, with a 

 few modifications, very much upon the same plan as that 

 in leaf buds. 



Returning to the expansion of the leaves, it may be 

 easily observed that the scales, which are mostly brown 

 and dry, do not expand, except in the forms intermediate 

 between the scale- and the ordinary foliage-leaf — but 

 rapidly fall away, leaving scars in the form of small, hard, 

 closely-set rings on the stem. They have admirably ful- 

 filled their purpose of sheltering the " winter-buds " from 

 the severity of the colder months (being absent from the 

 buds of plants growing in warm climates and from those 

 which are formed during the more genial parts of the 

 year, as in herbaceous plants) by many an ingenious 

 contrivance, such as hairs and gummy exudations which 

 render them bad conductors of heat and insoluble in water. 

 Nowhere is this object of protection more beautifully 

 carried out than in the bud of the ordinary Plane, which 



is completely covered by the hollow base of the leaf-stalk 

 at its junction with the stem, and is only revealed when 

 the winds of autumn bring down the leaves. It will 

 then be found to be wrapped in three coverings, an outer 

 of a gummy waterproof nature, a middle of furry scales, 

 and an inner of silky down. These scales may be com- 

 pared to those found on tubers and on underground stems; 

 and are in reality rudimentary leaves, transitional stages, 

 between their own form and that of the complete leaf, 

 being of common occurrence. According to Goebel, they 

 consist of chiefly of that portion of the leaf which first 

 arises from the growing point, and is known as the 

 " foliar base," which in an ordinary leaf develops so 

 slightly as to be hardly distinguishable from the fully 

 developed " upper leaf," and if a stalk be present it is 

 generally interposed between the two. This " foliar 

 base shows vigorous growth in the scales of the maple 

 and the horse-chestnut, the ordinary " upper leaf" being 

 sometimes so small as to require the microscope to make 

 it manifest, whilst other forms occur in which the latter 

 is easily distinguishable. To prove the origin of the scale 

 from the " foliar base " Goebel took several young plants 

 of the bird cherry (Primus padus) on the 14th April and 

 lopped off their apexes and part of their leaves. By the 

 10th of May the axillary buds, which should have expand- 

 ed next spring, stimulated to premature growth by the 

 excess of unused nourishment, began to develop vigor- 

 ously and normally ; the " foliar base," which usually 

 became scales, being transformed into foliage leaves. This 

 interesting experiment he afterwards confirmed upon the 

 horse-chestnut, the maple, the rose, and the oak. The 

 scales of certain plants are formed from stipules — small 

 foliaceous appendages often found at the bases of leaves 

 — as in the tulip-tree and many species of alder, where 

 the two stipules of the lowest leaf are modified into scales. 

 Resuming our study of the development of the 

 foliage-leaves, it will be found that their growth is much 

 more rapid than that of the stem, indeed the internodes, 

 or spaces between the nodes or attachment of the leaves, 

 in many plants remain as they generally are in the bud, 

 in an undeveloped condition, as in Nephrodium filix-mas, 

 or they may be so extremely short as to be apparently 

 wanting, as in plants which exhibit rosettes of leaves 

 (palms, etc.). In other cases, where the leaves are in 

 distant whorls, the internodes are formed immediately 

 after the leaves in the bud. In general, however, the 

 internodes in the fully-formed shoot are well-developed, 

 the nodes having sometimes a constricted and some- 

 times a swollen appearance, owing to the internal tissue 

 passing off into the leaves, complete rings being formed 

 when these encircle the stem, as in the bamboo and 

 grasses generally, and in some cases the node becomes a 

 separable joint, as found in the common pink. 



— o-^t^i^5tf-» — 



Middlesex Natural History and Science Society. — 

 This society held its first field-meeting of this summer 

 on Saturday last, assembling at Northwood Station. The 

 members walked through field paths to Batchworth Heath, 

 then skirting Bishop's Wood into Moor Park the walk was 

 continued into Rickmansworth. In the course of the 

 excursion Mr. Thomas Blashill instructed the members 

 on the methods of collecting and keeping wild plants to 

 form a herbarium. Dr. Wharton, who was associated 

 with Mr. Blashill as botanical mentor, contributed in like 

 manner to the instruction of the members. 



