LEAF-PROTECTION IN OLDENBURGIA ARBUSCULA DC. 



By Rev. Frederick Chari.es Kolbe, B.A., D.D. 



Among- the devices adopted by plants for self-protection, those 

 found in Oldenhurgia arhuscula DC., deserve special study. 



In this paper I limit myself to the lamina of the leaf. The 

 stem and petiole are provided with an extraordinary hypodermal 

 or cortical woolliness, the study of which would call for an inves- 

 tigation into development which I do not feel competent to under- 

 take. Nor do I know what has been published about the an- 

 atomy of this plant. My purpose is merely to sugg^est to teachers 

 the use of a native type of leaf-protection, which has not found 

 its way into the text-books, probably on account of its inaccessi- 

 bility in Europe or America. 



The plant grows on dry hill-sides near Grahamstown, fre- 

 quently in crevices or on ledges of rocks, and attains the dimen- 

 sions of a tree-shrub, as its name indicates. 



For purposes of comparison in the line of self-protection, we 

 can put as de Xerophytic and Halophytic structures, and con- 

 sider only those that arise from Sclerophyllous conditions. The 

 principal types are familiar enough to us— t<he minute, half-rolled 

 leaf of the Ericaceae (common to many of our orders) — the leaf 

 that can roll itself up at need (as in several grasses) — the com- 

 pletely cylindrical leaf of Bobartia or Hakea — the leaf that turns 

 its edges up to the sun (like many Proteas) — the leaf that buries 

 its stomata in woolly pits (Nerium Oleander) — the leaf that hides 

 its green and clothes itself in silk (like the wSilver-tree) — and so 

 forth. 



With all tlieir success, every one of these plants makes some 

 confession of weakness. Either they hide their green, or refuse 

 to face the sun, or diminish their size, or breathe with timidity 

 through minute stomata with small air-spaces behind them. The 

 Oldenhurgia displays none of these weaknesses. Its brilliant 

 green leaf faces the full glare of the sun, and is larger than most 

 leaves of the sheltered forest. Its stomata are numerous, and 

 of more than average size, and arc, moreover, not only not hidden 

 in recesses, but actually protrude above the surface. And by 

 protruding I do not mean that there is an arched chimney of 

 cuticle, as in the Proteaceae ; the guard-cells themselves rise 

 above the rest of the epidermis. Lastly, chief audacity of all, its 

 spongy tissue, so far from being closely packed, is made up of 

 stellate cells, which stretch out long arms to one another as they 

 do in many water-plants. It looks as if the Oldenhurgia has 

 over-protected itself, and scornfully treats its dry hill-side as if if 

 w^ere the marshy top of Table Mountain. 



