[ 255 | 
Р, 
IX. On Bud-protection in Dicotyledons. By Percy Groom, B.A., Frank Smart 
Student, Gonville and Caius College, Cambridge. (Communicated by D. Н. 
Scorr, MA., Ph.D., F.L.S.) 
(Plates LIX. & LX.) (2 
Read 18th February, 1892. 
THE welfare, or even the very existence, of a plant is dependent on the preservation 
of the young growing parts of the shoot. Yet several circumstances conspire to render 
the life of the bud precarious. A growing bud is more or less exposed in position, 
and necessarily delicate in structure: hence it is peculiarly liable to physical injury 
from excess of light, extremes of temperature, and loss of indispensable water. For the 
same reasons buds are rendered an easier prey to hostile organisms, whilst the nutritious 
nature of their contents even invites attack. Not only do these young parts of a plant 
require protection, it is also imperative that the protective mechanism should be of such 
a sort as to permit of simultaneous or, at any rate, subsequent growth: hence many of 
the protective measures adopted by mature organs are out of the question. 
The most striking illustrations of bud-protection are to be seen when the environment 
is peculiar. When plants are exposed alternately to a favourable and an unfavourable 
season, there is frequently a wide difference between the actively growing buds and the 
“resting buds.” Тһе latter are often covered by an envelope of scale-leaves, by 
persistent petioles, peculiar prophylla, modified stipules (1), &c. Goebel has described 
the careful manner in which the growing-point and young leaves of succulent plants are 
buried in the older tissue (13). These cases may be contrasted with those of plants 
growing under favourable conditions. Submerged plants and many plants growing in a 
perennially moist and warm region (5) have buds of loosely-packed leaves, so that 
the growing-point is all but exposed. But the means of bud-protection adopted by 
a plant depend as much on the character of the plant as on the environment. 
Marchantia, though growing in moist and shady places, possesses an elaborate arrange- 
ment of amphigastria curled over the growing-point and a thick coating of mucilage 
over the young tissue: the reason of this is that Marchantia is very sensitive to loss of 
_ moisture. | 
The need for protection on the part of the growing-point and younger leaves explains 
at once the fact that older leaves cover the younger leaves at the end of the shoot—in 
fact, that a “bud” is formed in order to permit the younger leaves developing as far as 
possible under the shelter of the older leaves; they are closely packed and often folded 
so as to take up the least room possible inside the bud (3). Frequently, too, when the 
outside leaves of а bud expand, the blades of the younger leaves are not immediately 
exposed in consequence: the latter may be covered by their own stipules (2), or they 
SECOND SERIES.—BOTANY, VOL. III. 20 
