150 MORPHOLOGY OF MEMBERS. 



the green organs which have been termed simply leaves (foliage-leaves). All 

 these structures are therefore also called Leaves {Phyllomes) ; and this designa- 

 tion is frequently justified by the fact that many of these organs actually become 

 transformed, under peculiar conditions, into green leaves. Since the green organs 

 which are termed leaves in popular language (foliage-leaves) may be considered 

 as leaves par excellence, the other structures, which are also considered to be 

 foliar, are termed metamorphosed leaves. The same is also the case with those 

 parts to which the leaves are attached, and on which they grow as lateral ap- 

 pendages. They sometimes have the form of cylindrical or prismatic, slender, 

 greatly elongated stems, sometimes of thick roundish tubers, or are often hard 

 and lignified (trunks) ; in other cases they are soft and flexible, either embracing 

 other firm bodies (bines), or firmly attached "to them, as in the ivy; they may 

 also occur as sharp spines or tendrils (grape-vine). All this is connected with 

 the mode of life of the plant, and with the functions of the structures under 

 consideration. But if the one characteristic only is kept in view, that they all bear 

 leaves which arise below their growdng apices, an agreement is found as important 

 as complete, which may for the time be altogether abstracted from the physio- 

 logical functions and the corresponding structure ; and when once this abstraction 

 is made, the agreement may be denoted by applying a common name to all those 

 parts which bear leaves ; they may be termed Stem-structures {Caulomes) or simply 

 Axes. In the same sense therefore in which, for example, the tendril of a pea is a 

 leaf, the tuber of a potato is also a stem or axial structure ; and just as the tendril of 

 a pea is termed a metamorphosed leaf, so the tuber of a potato may also be called a 

 metamorphosed stem. 



The same is the case with hairs as with leaves and stems; the distinguishing 

 characters of root-hairs, woolly hairs, prickles, glandular hairs, &c., is that they all 

 originate as outgrowths of epidermal cells. If we now go a step further, we may term 

 all appendages of other parts which originate as outgrowths of epidermal cells, 

 whatever their form and function, Hairs {Trichomes). Thus the so-called paleae and 

 the sporangia of Ferns are trichomes ; or, if the ordinary filiform hairs are considered 

 the original form, they are then metamorphosed hairs. It does not necessarily follow 

 that hairs grow from a true epidermis ; it is held sufficient if they arise from single 

 superficial cells ; and thus the number of the external appendages termed trichomes 

 is still further increased. 



As in the case of stems, leaves, and hairs, we may speak also of metamorphosed 

 roots ; they are usually filiform, long, and slender, but sometimes thick and tuberous ; 

 usually they grow beneath the ground, but also sometimes above ground, and even in 

 an upward direction. Nevertheless, under all circumstances roots maintain so striking 

 a similarity to their typical forms, that the term metamorphosed is but seldom ap- 

 plied to them. 



This mode of investigation, applied to Vascular Cryptogams and Phanerogams, 

 has shown that all the organs of these plants may be referred to one of these 

 morphological categories; every organ is either Stem (Axis), Root, Leaf, or Hair. 

 The Muscineae have no roots in a morphological sense, although they possess 

 organs which completely fulfil the functions of roots ; on the other hand most have 

 leaves which grow on stems (axes). In Algae, Fungi, and Lichens, the plant has 



