a 14 MORPHOLOGY OF MEMBERS. 



The foliage-leaves'^ are always distinguished by their green colour, owing to 

 their containing chlorophyll (which however is sometimes concealed by red sap); 

 and it is these which, in popular language, are exclusively called leaves. Usually 

 they are the largest foliar organs of the plant, lasting the longest, and distinguished 

 by the greater degree of segmentation of the outline, as well as by the more perfect 

 development of their tissue. As the chief store-houses of chlorophyll they are the 

 most important organs of assimilation, and are always destined to be expanded to the 

 light even when they are formed on underground growing points (as in Sabal, Pieris 

 aquilina, &c.). When small they are usually produced in great numbers on a shoot ; 

 as they increase in size their number and the rapidity of their growth diminishes in 

 proportion. In this respect the numerous small leaves of Mosses may be compared 

 with the few large leaves of Ferns, the numerous small leaves of Conifers with the 

 few large ones of Cycads, &c. 



Scale- or Cataphyllary leaves are usually produced on underground shoots, 

 and remain buried in the earth, although they also frequently occur above ground, 

 especially as an envelope to the winter-buds of woody plants (as the Horse -Chesnut, 

 Oak, &c.). In the genus Pimis the primary and strong lateral axes form leaves 

 of this kind only ; the acicular foliage-leaves appear in tufts on small axillary 

 shoots; in Cycqs scale-leaves alternate regularly on the stem with large foliage- 

 leaves, Seedlings (as of the Oak) and the lateral shoots from underground axes 

 often begin with scales and only advance at a later period to the production of 

 foliage-leaves {e. g. Struthiopteris, jEgopodiutn, Orchis, Polygonatum, &c.). In 

 parasites and plants which live on decaying vegetable matter (saprophytes) and 

 are destitute of chlorophyll {e.g. Monotropa, Neottia, Corallorhiza, Orobanche, &c.) 

 the scales are the only foliar structures of the vegetative parts, the foliage-leaves being 

 absent. Even in those plants whose foliage-leaves are much segmented the scales 

 remain simple ; they are distinguished by a broad base, usually diminutive length, 

 the absence of prominent veins, and by forming no chlorophyll or only very little. 

 They are colourless, yellowish, reddish, or often brown ; their texture is, according 

 to circumstances, fleshy, succulent (as in some bulbs), membranous, or tough like 

 leather. 



In Phanerogams, especially in Monocotyledons and Dicotyledons, several other 

 forms of leaves make their appearance as a preliminary to fertilisation — bracts, 

 sepals, petals, stamens, and carpels. The thick seed-leaves or cotyledons will be 

 spoken of in detail as a peculiarity of these classes. 



From the point of view of the Theory of Descent we are justified in considering 

 all other forms of leaves as subsequent metamorphoses of foliage-leaves ; and these 

 latter are therefore regarded as the original typical leaves. When they lost their 

 original function — the assimilation of food-materials — and served other purposes, 

 they assumed at the same time other forms and structure. The same is meant 

 when certain tendrils and spines are said to be metamorphosed leaves. Leaf-tendrils 



Laubblatt by ' hypsophyll,' 'cataphyll,' and 'euphyll.' The two first of these are useful arlditions 

 to botanical terminology ; the last, however, does not seem to be required, being precisely equivalent 

 to the term foliage-leaf, which is already in general use (hypsophyll = bract)]. 



^ Compare the characteristics of the formations of leaves in A. Braun, Verjiingung in der 

 Natur, Freiburg 1849-50, p. 66. [Ray Soc, Bot. and Phys. Mem. 1853, p. 62.] 



