2l8 



SCIENCE-GOSSIP. 



vogue, as the " Hypopodium." The slight basal 

 swelling we find on many leaves, just at their 

 attachment to the stem and which we term the 

 " pulvinus " (e.g. poplar), is an example of a some- 

 what profusely developed leaf-base ; the spines of 

 the gooseberry tree are hypopodia which have 

 undergone a remarkable alteration. 



12 3 + 



Fig. 4. — Development of lamina on bud-scale of sycamore. 



The foliar bases in many cases undergo a further 

 process of segmentation, so that they bear a pair of 

 lateral appendages termed the " stipules." The 

 upper region into which the primordial leaf is 

 differentiated suffers many changes, finally to 

 appear as the " leaf -blade " or " epipodium." 

 Between these two parts a third zone may or may 

 not, according to circumstances, be intercalated. 

 This portion present forms the "leaf-stalk" or 

 " mesopodium." (See fig. 1.) 



It is by suppresion, unusual growth or structural 

 modification of one or more of these foliar regions 

 that the appearance of bud-scales is to be explained. 

 It is always the oldest and therefore lowest leaves 

 arising from the growing point which are thus 

 changed. I have been much interested in the 

 question of the nature of these protective mem- 

 branes of the young shoot, and have during last 

 spring found much amusement and instruction in 

 carefully watching buds of various kinds as they 

 expanded. The result of a few of these observa- 

 tions, if I may so term the recordance of such very 

 evident facts, is contained in the sketches accom- 

 panying these remarks. We may consider the 

 changes which the leaf-parts undergo, to adapt 



them to their protective function, under four 

 headings : 



I. — Bud-scale — Leaf-blade or Epipodium. 



It may happen that the leaf-blade remains small 

 and becomes more or less scaly in its texture, 

 whilst the stalk is entirely arrested. Such a con- 

 dition is found in the lilac, the privet, the catalpa, 

 the walnut, etc. (See fig. 6.) In the lilac the 

 usual rule is that the bud-covering becomes a full 

 green and enlarges considerably, showing to a 

 greater or less extent its relationship to the 

 ordinary foliage-leaf ; the petiole (stalk), however, 

 does not usually appear. In some few instances, 

 however, there is a more complete development in 

 which the scale becomes an almost normal foliage- 

 leaf with a stalk (see fig. 2.), and other characters 

 present. 



II. — Bud-scale — Leaf-base or Hypopodium. 



In these instances it is by this unusual growth of 

 the foliar-base and its assumption of a membranous 

 nature that the scale is to be explained. As 

 examples may be cited the horse-chestnut (fig. 3), 

 sycamore (fig. 4), black currant (fig. 5). Primus 

 padus, etc. The leaf-blade and stalk are not 



1 Z 3 ^ 



Fig. 6. — Development of bud-scale of walnut. 



Fig. 5. — Development of lamina on bud-scale of black- 

 currant. 



developed, and an indication of them can only be 

 perceived by microscopic investigation. Exceptions, 

 however, occur in which the scale does not drop off 

 at the opening of the bud, but persists for some 

 little time. In these cases the prolonged supply of 

 nourishment apparently stimulates the ordinarily 

 suppressed parts to further growth, and the leaf- 

 blade, often of some size, may be seen springing 

 from the scale (see figs. 3, 4 and 5). In the black- 

 currant this secondary growth would seem to be the 

 rule rather than the exception. 



III. — Bud-scale — Stipules of Lowest Leaves. 

 Under this head we include those cases in which 

 the stipules of the leaves which are lowest on the 

 shoot become modified to form enveloping scales 

 for the younger leaves above. Such a condition 

 occurs in the buds of elm, lime, hazel, Spanish chest- 

 nut and Portugal laurel (see fig. 7, a and b). If buds 

 of these trees be carefully watched as they expand, 



