SCALE-LKAVES, FOLIAtiE-LEAVES, FLOKAL-LEAVES. 1339 



tlie winter, with utulergrouiul buds or Imllis, the young sprouting foliage-leaves Jo 

 not have this assistauce; the}- must carve their way through the soil unaided, and 

 press above the surface without a sheathing envelope. Accordingly they have to 

 bore thraugh a more or less thick layer of earth, often a stiff clay; or one perhaps 

 containing pointed stones and angular grains of sand. Now in order that the 

 foliage-leaves traversing this rugged and uneven path may suffer no damage, they 

 are variously fokled and twisted together so as to form a cone; and most important 

 of all, the apex of this cone, which operates like a ground-auger, and therefore 

 exercises a strong pressure on the soil, is armed with special cells. These cells 

 have a great resemblance to those at the apex of the sheath-like scale-leaves, and to 

 those of the knee-shaped bent cotyledon oi the onion (see p. GOG). In many ])laiits 

 possessing lobed or deeply-divided leaf-blades, the boring apex of this cone is formed 

 by a bend of the leaf-stalk, which is doubled over like a hook. Thus in the foliage- 

 leaves of the Yellow Monkshood (AconituTn Vulparia, Lycoctonum, &c.) it is not 

 the apex of the leaf which emerges first from the ground but the convex part of 

 its lient and knee-like stalk. As long as the leaf is still occupied in boring, the 

 delicate free apices of its lobes are directed inwards and downwards, and not until 

 the hooked leaf-stalk has emerged above the surface of the soil does it straiohten 

 and draw the leaf-blade out of the ground. The free points of the leaf-blade, which 

 were hitherto directed downwards, are inclined in the opposite direction when 

 they arrive above the earth, and the whole leaf then unfolds into an expansion 

 parallel to the surface of the ground. An exactly similar process is observed in 

 large ferns with undei-ground winter buds, e.g. in the common Male-fern {Aspidiiiin 

 FiUx-raas). The fronds at the end of the root-stock are .spirally rolled, their 

 delicate segments are packed closely together, one above the other, and covered by 

 the sti'ong rachis of the leaf as by a thick hoop. Only the back of this rachis 

 comes into contact with the forest soil as it is broken through; the rachis prises up 

 the top layer of the soil in its gradual unrolling, and the delicate segments are only 

 unfolded when the part of the axis in question has emerged and straightened itself. 

 The earth is broken through in a very peculiar manner by the peltate leaf- 

 blades of Podophyllum peltahom. As long as the leaves of this plant are still 

 small and below the gi-ound, they resemble a closed umbrella; the folded blade is 

 directed downwards, and nestles close to the thick stalk, which grows straight up. 

 At the free end of the stalk, which would correspond in position to the ferule of an 

 umbrella held upright, is found a group of thin-walled, turgid cells, without chloro- 

 phyll, situated like a white knob at the convorging-point of the leaf-strands. When 

 the leaf-stalk grows in height, it is this cell-group wliich presses on the layers of earth 

 above it, and it is the first to appear at the surface. The leaf-blade, still furled to 

 the stalk, is then raised up through the hole thus bored. Once above the surface, the 

 blade expands just like an opening umbrella. The above-mentioned group of cells, 

 having served as a buffer, now loses its turgescence, but remains visible as a white 

 spot at the centre of the brownish-green expanded leaf -blade. In the species of the 

 genera Acanthus and Ilydrophyllum, which are characterized b^- divided leaves. 



