660 STEMS BEARING FOLIAGE-LEAVES. 



palms, dracaenas, and species of Yucca, of which the Yucca gloriosa, illustrated in 

 fig. 154, may serve as a type, exhibit a very peculiar structure. The yearly 

 increase in length of the stem is comparatively small, the leaves which project all 

 round from this portion of the stem are consequently crowded together and form a 

 rosette which cannot be distinguished as regards the arrangement of the individual 

 pai-ts from the radical i-osettes of Agaves and species of house-leek, and, like these, 

 must be regarded as a short axis. In the following year the stem continues this 

 curious, abbreviated growth, the foliage-leaves of the previous year gradually die 

 off, and only the hardened remnants of their leaf-bases are left behind, thus the 

 rosette or head of fresh green leaves is now seen borne by a naked columnar stem. 

 This continues for many years, and the gigantic crown of leaves rises higher and 

 higher above the ground. Plants with this manner of growth, moreover, never 

 attain even in many years to anything like the height which is attained by foliage- 

 stems terminating in or branching out into long axes. Even the tallest palm 

 terminating in a short axis is a dwarf in comparison with the rotangs or climb- 

 ing palms, continually shooting out long axes. Rotang stems are known to extend 

 to almost 200 metres. The length of 200 metres is perhaps the extreme limit 

 reached by a foliage-stem, and if we again contrast the extreme cases, and compare 

 with these climbing palms the stems of the minute Gentiana nana growing on the 

 high Alps, it is seen that the shortest known of all foliage-stems is exceeded by the 

 longest about twenty thousand times, in round numbers. 



The ramification and facies of foliage-stems is in main part governed by the 

 light-requirement of the leaves they bear. Necessarily the foliage-stem as the 

 bearer of organs which have to prepare organic materials in the sunlight is chiefly 

 influenced in its growth, and as to the position which its branches assume by the 

 conditions of illumination. In order that all the green leaf-blades of a plant 

 may be suitably illuminated, it is necessary that all these foliar axes should be 

 grouped conformably, and should divide up the space most economically. Where 

 foliage is chiefly borne on short branches, even under the most favourable condi- 

 tions, only a relatively circumscribed space can be utilized. But when the reverse 

 is the case and foliage is produced on long branches, the plant is much more 

 favourably circumstanced. Such plants can unfold their leaves gradually above 

 one another, and display them at appropriate intervals and distances to the sun- 

 light. This elevation of the leafage above the ground is rendered possible either 

 by the possession of a specially-contrived stem, or through the employment by the 

 stem of some strong substratum or support up which it climbs to the light. 

 Again, long axes, which have not the capacity of rising above the ground in 

 either of these ways can elongate while embedded in the soil or extended on it, 

 and, running out in all directions, can arrange their green leaves in a mosaic-like 

 carpet. Lastly the foliage-stems can be sustained in the position most suitable to 

 their leaves by means of the surrounding water. According to the circumstances, 

 foliage-stems may be broadly classed in four groups, viz. those which lie on the 

 ground (stirpes procumbentes), those which float in water (stirpes fliictuantes). 



