CHARACTERISTIC FORMS OF LEAVES AND SHOOTS. 1 93 



of vascular plants, and is often very characteristic of large groups. This will be 

 explained more in detail in the proper place. 



In Characeae, Muscineae, and Vascular Cryptogams, all the leaves of a plant 

 are usually similar, being either simple or segmented in the same manner, although 

 the segmentation, especially in Ferns and Rhizocarps, is simpler in young plants 

 and in those that are still weak than in the large leaves of mature plants. But it also 

 happens, even in Cryptogams, that leaves of very different forms are found on the 

 same plant. Thus some Mosses form colourless minute leaves on the underground 

 creeping shoots, while in the neighbourhood of the organs of reproduction they often 

 produce leaves of a different shape from those on the rest of the upright parts of the 

 shoot. In the same manner the leaves on the underground shoots (stolons) of 

 Struthiopteris germanica remain as thin membranous scales, which are replaced 

 on the upright end of the stolon by large green pinnate leaves. In Salvinia each 

 whorl forms two simple roundish leaves which rise into the air, and one that hangs 

 down into the water and consists of filiform branches. Even in Coniferse and 

 Cycadeae the variation in the leaves of one plant is much more common ; while 

 in Monocotyledons and Dicotyledons the shapes of leaves become extraordinarily 

 variable, not only on the same plant but often on the same shoot. 



. The two most common forms of leaves are the Scales or ' Cataphyllary leaves' \ 

 and the Foliage-leaves. '. i 



The Foliage-leaves - are always distinguished by their green colour, owing to 

 their containing abundance of chlorophyll (which however is sometimes concealed 

 by red sap). It is these which, in popular language, are exclusively called leaves, 

 and in descriptive botany are designated by the term ' folium/ 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 more perfect formation 

 of their tissue. As the chief vehicles 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 piuicla vegetatimiis (as in Sabal, Pteris 

 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. 



^^(7^- or ' Calaphyllary-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-chestnut, 

 oak, &c.). In the genus Pinus the primary stem and the strong lateral shoots form 

 leaves of this kind only ; the foliage-leaves appear on small axillary shoots (as tufts 



' [Henfrey, in his translation of Braun's 'Rejuvenescence in Nature' (Ray Soc, Botanical and 

 Physiological Memoirs, 1853), first proposed to render the terms Hochblatt, Niederblatt, and 

 Laubblatt by ' Hypsophyll,' ' Cataphyll,' and ' Euphyll.' The two first of these are useful additions 

 to botanical terminology ; the last, however, does not seem to the present translator to be required, 

 being precisely equivalent to the term Foliage-leaf, which is already in general use.] 



2 Compare the characteristics of the formations of leaves in A. Braun, Verjungung in der 

 Natur, p. 66. Freiburg 1849-50. [Ray Soc, Bot. and Phys. Mem. 18^; 3, p. 62.] 



O 



