658 STEMS BEARING FOLIAGE-LEAVES. 



mum about half-way up. Very often an unequal thickening may be observed in 

 the foliage-stem; this is due to the fact that at the places where leaves arise from 

 the stem knotty swellings are developed, while those portions of the stem which 

 come between successive leaf -insertions (or nodes), and which are called internodes, 

 are cylindrical or prismatic in form. A foliage-stem which has this peculiarity is 

 said to be " nodose " (nodosus). Sometimes the internodes of such nodose stems 

 adjoin one another at obtuse angles, and such a stem is then called in botanical 

 terminology " zigzag " (flexuosus). 



The fully-developed internodes of which the foliage-stem is built up, are only 

 rarely, and then only for short distances, of precisely equal length. Sometimes 

 longer and shorter internodes alternate, and quite as often it happens that a single 

 much-elongated internode succeeds several short ones. If such an elongated inter- 

 node passes over into the region of the flowers, it is known as a " scape " (scapus). 

 As in the scaly stems, where short and long axes can be distinguished, so is it with 

 the foliage-stem. The leaves are usually so crowded on these short axes that they 

 form rosettes or fascicles which quite cover the stem which bears them. On the 

 other hand, on many long axes the leaves are developed scantily and at long 

 intervals and we are tempted at first glance to take such an elongated shoot for 

 the leafless stem of a switch-plant. A large number of plants develop in one year 

 only short axes with rosette-like radical foliage-leaves ; in the following year 

 the apex of the short axis grows up into a slender, elongated shoot which passes 

 above into a floral stem. This is the case in most plants whose stem is said to he 

 " biennial " (stirps biennis). Similar conditions are observed, however, in many 

 perennial species of house-leek (Sempervivum), Aloe, and various other plants with 

 fleshy, succulent leaves, only in these the alternation of long and short axes extends 

 over several, often very many years. A vf^.ry noticeable form of this kind is 

 Agave Americana, known by the name of the "Century Plant", illustrated in 

 fig. 153. Often 20, 30, even, it is alleged, 100 years pass by, during which long 

 period the plant produces only a short stumpy axis beset with leaves grouped 

 in a rosette. At length a long axis arises from the centre of the rosette and 

 terminates in a voluminous inflorescence. As soon as the fruits have been pro- 

 duced from the flowers, and the seeds have escaped, not only the long axis, as 

 in biennial plants, but also the short axis with its large, stiff and spiny rosette- 

 leaves entirely dies away. In water-plants this type is also met with in the 

 remarkable Water Soldier {Stratiotes aloides), to which allusion has been so 

 frequently made. In this plant, as in the house-leeks and saxifrages, long axes 

 which continue to grow until they have arrived beyond the circle of the whole 

 rosette, arise from the axils of the lower leaves; when this has happened, the 

 young horizontally-projecting shoot stops extending, and at its tip again forms a 

 - short axis, i.e. a rosette, which, in the following year, sends up a fresh long axis. 

 A similar alternation of long and short axes is also observable in numerous other 

 plants, in the shrubby spiraeas, and in roses, hawthorn, sea-buckthorn, barberry, and 

 Astragalus, which we shall encounter later on as hedge-forming shrubs. Some- 



