5o6 LECTURE XXX, 



between the normal green leaves and the scales of winter-buds which envelope the 

 young foliage-leaves until the next period of vegetation (cf. Fig. 301). He shows 

 in the first place, by simple observation, that the bud-scales as well as the small 

 scale-like leaves of the subterranean shoots of many plants are according to their 

 origin and as a matter of fact ordinary foliage leaves, which, however, during further 

 development are arrested in so far that the blade of 'the leaf (lamina) very soon 

 ceases to grow, often even when it is not yet, or is scarcely, visible ; whereas a lower 

 portion of the leaf, which is but little or not at all developed in normal leaves-^the 

 so-called leaf-base— in many cases grows up vigorously and constitutes the body 

 of the scale proper. 



In order to examine the matter more closely, it must be noticed in the first 

 place that Eichler established, so long ago as 1861, that two or three stages must be 

 distinguished in the development *of a leaf. The body which comes forth imme- 

 diately from the growing-point of the shoot as the leaf, is termed by Eichler the 

 primordial leaf: it appears as acrescentic or annular cushion of embryonic tissue. 

 This primordial leaf becomes segmented in the first place into two chief portions ; 

 a stationary zone, which takes no further part in the formation of the leaf, and 

 a portion which gives rise to the leaf proper. The former is the foliar base, the 

 latter the so-called upper-leaf, from which the blade of the leaf arises in every case : 

 when a petiole is developed it is intercalated, as it were, subsequently, between the 

 foliar base and the young lamina. Goebel shows now that the scales on the winter- 

 buds of Syringa, Lonicera, Daphne, and others, come into existence by the rudi- 

 ments of the foliage-leaves being arrested at a middle stage of their development, 

 the formation of the otherwise normal petiole being altogether suppressed. 



A second category of bud-scales is found in the species of Maple, Horse- 

 chestnut, and other trees. In these cases the bud-scale arises by the above-named 

 foliar base of the primordial leaf developing vigorously while the lamina of 

 the leaf, though it exists in a rudimentary state, is soon arrested, and may then 

 be detected at the apex of the scale by means of the microscope. If sprouting 

 winter-buds of the Maple and Horse-chestnut are examined in the spring, 

 intermediate forms between ordinary bud-scales and foliage-leaves may often be 

 found; the scale-like portion (that is the developed foliar base) is then smaller, 

 but the arrested lamina is so large that it can be recognised at once as a 

 foliage-leaf. 



In a third category of winter-buds, it is from the so-called stipules — ^that is, leaf-like 

 structures which protrude laterally right and left from the foliar base at the sides of 

 the leaf proper — that the bud-scales arise. In various species of Alnus and 

 in the Tulip-tree, the enveloping of the winter-buds is effected simply by the 

 lowermost, tolerably normally developed foliage-leaf having its two stipules modified 

 in the form of bud-scales. In our native Oaks also, and in the White Beech and 

 Red Beech, it is the stipules of arrested foliage-leaves which envelope the winter- 

 buds ; in these cases, however, the laminae of the leaves in question are completely 

 arrested very early, although their true nature can still be distinctly perceived by 

 means of the microscope. Even the bud-scales of those Coniferae and Cycadeae 

 which form resting-buds are, according to Goebel's investigations, simply modified 

 foliage-leaves. Of subterranean scales, those on the rhizomes of Dentaria, Chrysos- 



