256 MR. PERCY GROOM ON BUD-PROTECTION IN DICOTYLEDONS. 
may be protected by outgrowths from the base of older leaves (e. в. Clusia, Taberne- 
montana, Fagrea) and the outgrowths may take the definite form of stipules. 
But the most critical time for the young leaves is when they are first exposed, their 
epidermal walls being thin and feebly euticularized, and their chlorophyll dilute and 
easily decomposed. То avoid excess of light these youngest exposed leaves are frequently 
directed vertically. Often, too, this arrangement is associated with a diminution of the 
transpiring surface caused by a folding of the lamina or the close contact of two leaves. 
In many plants with opposite leaves, the two outermost leaves of a bud are directed 
vertically with their inner faces in close contact (e.g. many Rubiacee, Clusia sp., 
Bucklandia populnea, В. Br., Veronica imperialis). In Durio zibethinus the pendent 
arrangement of the conduplicate young leaves gives a characteristic appearance to the 
tree. In some plants with stalked leaves the change of direction of the lamina leads 
to the older leaves at the end of a shoot forming an umbrella-like screen over the 
youngest exposed leaves (е. g. Gossypium, Dombeya Mastersii, species of Abutilon, 
Hura crepitans, Begonia sp.). Frequently the young leaves are coated with glistening 
hairs. That these hairs perform their functions whilst the leaves are young, is proved by 
the fact that the older leaves may be apparently quite glabrous. One of the functions 
of these hairs is to protect the young leaves, for they diminish transpiration and 
radiation and reflect light. The young leaves of many plants are rendered conspicuous 
by their colour, being generally red, reddish brown, or brown. These colorations are 
especially common in plants exposed to strong sunlight, $. е. alpine plants and tropical 
plants (е. g. sp. of 1тоға, Calophyllum, Treculia africana, Decne., Garcinia Cambogia 
var. papilla, Nephelium Litchi, Clusia вр., Wormia Burbidgei). Various experiments 
make it probable that these colouring-matters protect the young leaves from excess 
of light (16). At the same time they шау be merely the unavoidable results of meta- 
bolism, or have some other significance ; for we find that the colour is often due to the 
presence of tannin or tannin-like bodies. Also similar red colouring-matters are found 
on parts not exposed to light, e.g. in villous colleters, &с. (Cosmibuena, Hoffmannia). 
These villi are not manufacturing the colouring-matters for the use of the young leaves ; 
for, as far as I could see, the colouring-matters were never transported from the 
colleters : in addition the leaves of Cosmibuena are green when they emerge. 
.. Many buds have a great protective auxiliary in the secretion which covers and fills 
them. ‘This secretion consists of gummy mucilage or resin, or both together (7 & 17); 
it is secreted by the general epidermis, by colleters, or by **leaf-teeth." These “ blasto- 
colla ”-secreting glands are characterized by their early development and their short- 
lived activity. The colleters, further, occur only on that essentially protective organ, 
the leaf-base, or on its outgrowths (stipules). After functioning for a short time the 
eolleters, and often the stipules which bear them, dry up or drop off. These facts 
sufficiently indicate that these external secretory organs are definitely formed for 
the sake of the bud. It is, unfortunately, impossible to excise these structures early, 
and thus give confirmatory evidence of their importance to the bud; I did, however, 
remove the secretory hairs of the youngest exposed leaves of a species of Ochna. The 
hairs occur at the margin of the leaf and only secrete in the bud, and not later in life. 
