SCALE-LEAVES, FOLIAGE-LEAVES, FLORAL-LEAVES. 625 



the scale-leaves principally function as protecting envelopes for the foliage- 

 leaves. The young and still very delicate foliage-leaves, folded together within 

 the bud, are entirely surrounded and over-arched by them. The sheath-like 

 scales close together like a dome over the bud, and form an actual shield for 

 it. Either hard, much-thickened cells, or more usually, strongly turgescent 

 cells are present at the apex of each of these scale-leaves, and often these 

 coverings are injured in penetrating the soil ; but this is not of great import- 

 ance because the scale -leaves become superfluous and perish when once the 

 foliage -leaves have emerged and expanded above the ground. If earth is 

 thrown up over the underground stock of such a plant as the Rhubarb, 

 the scale-leaves of the turions increase in length in proportion to the thickness 

 of the heaped -up stratum. The growth of the leaves keeps pace with the 

 growth of the enveloped shoot ; scarcely has the earth been penetrated when 

 the scale-leaves stop growing, and the shoot — no longer requiring a protection 

 against the ruggedness of the soil — rises up from its sheathing envelope and 

 unfolds its young, green foliage - leaves in the sunlight. If the layer of earth 

 which has been piled up above the subterranean stock is too thick, and if the 

 store of building -materials for the lengthening of the sheathing scale -leaves 

 is inadequate, then the young, green foliage -leaves are forced to leave their 

 protecting envelopes even below the ground, and make their appearance above 

 usually damaged, torn, and mutilated. Many fumitories (e.g. Corydalis fabacea) 

 have only a single sheathing scale-leaf which surrounds that part of the shoot 

 possessing green foliage - leaves. Here also it can be plainly seen that the 

 scale - leaf affords protection only as long as it is necessary, i.e. the scale 

 stretches up from the lowest portion of the shoot-axis until it has reached the 

 surface of the ground, where the delicate, green foliage-leaves no longer require 

 protection, and can unfold in the air. If the Corydalis is rooted only super- 

 ficially in the earth, the scale-leaf is raised a very little, often scarcely a single 

 centimeter, but if it is very deeply rooted, or if earth is heaped up over it 

 either purposely or accidentally, then this lengthening of the lower portion 

 of the stem amounts sometimes to more than 20 centimeters. In either case 

 that portion of the stem by which the sheathing scale-leaf is raised stops 

 growing as soon as the apex of the sheathing envelope has reached the surface 

 of the soil, and it looks as if the Corydalis had deliberately adapted itself to 

 the existing conditions. 



Many plants have two kinds of underground scale -leaves. Firstly, those 

 whose cells are filled with starch and other food -reserves. These are always 

 thick and fleshy, and they do not continue to grow, but are absorbed by the 

 growing shoots. Secondly, sheath-like ones, which elongate, inclose, and protect 

 the green foliage- or floral-leaves, in their passage through the layers of eai-th 

 as they grow up towards the light ; these do not cease growing nor lose their 

 turgescence until the delicate structures within reach the surface, when they 

 are in no more danger, and require protection no longei'. 



Vol. I. 40 



