STRUCTURE OF SHOOT-AXES. 



45 



vascular bundles, in part in the parenchyma between these, and from which true 

 wood-tissue is produced towards the inside, and so-called secondary cortex towards 

 the outside. In this way, the originally tender shoot-axes of the plants named become 

 transformed into solid, persistent, woody stems and branches, from which the leaves 

 fall later on, and which serve henceforward only as supports for the shoots existing 

 for the time being. In the stems of Palms and Ferns; such a secondary formation 



Fig 39- — Cvcus reruns: A corn seen from above, B from below, C from the side, and in longitudinal section. The 

 ring-like lines of insertion of the cataphyllary leaves are seen a\.f,f,f, and at k, k the aTillary buds belonging to them ; b 

 base of decayed flower, and leaf-stem, by its side hk (in C), the bud which will replace it, from which a new corm and flower- 

 stem will arise. D longitudinal section through this bud ; «, n its cataphyllary leaves ; /, I foliage-leaves ; A bract ; 

 / perianth ; a. anthers ; £ a bud in the axil of a foliage-leaf, 



of wood and cortex by means of ^ cambium does not take place. In them, the 

 shoot-axis is at once from the beginning so thick, and so penetrated by bundles 

 and layers of elastic fibres, that it is able, with progressive elongation of the 

 stems, to bear the burden of the leaves arising 

 at the apex. It would carry us much too far 

 to go more closely into the anatomical and 

 exceedingly various relations of organisation 

 of shoot-axes. The main point for physiologi- 

 cal consideration is, that, as supporters of the 

 leaves, and, later on, of entire and often huge 

 branch-systems, they must possess not only 

 the necessary solidity, which is afforded 

 by, true wood "or by numerous bundles of 

 elastic fibres; but provision must also be made, 

 that the water taken up by the roots, ascend- 

 ing in the woody parts, is not evaporated on 

 its way through the stem and the shoot- 

 axes. This is suflBciently provided against 

 in younger shoots by the epidermis, in older 



ones by the cork-periderm, and in the very old ones by the solid bark. Another 

 function of the shoot-axes is, finally, to convey the substance assimilated by the foKage- 

 leaves, on the one hand to the root, and on the other to the buds and shoots ; this is 

 accomplished in part by means of the so-called phloem (soft-bast) of the vascular 

 bundles, or the secondary cortex, in part by the parenchymatous fundamental tissue. 

 If the variety of form of the . shoot-axis makes itself evident especially in 



Fig. 40. — Bud in interior of bulb oiAUtum. Cepa, after 

 removal of the scales, st broad, short part of stem on 

 which the scales are insetted ; I (in A) lamina ; sh the still 

 short sheath of foliage leaves. In B the outer leaves have 

 been removed, and an axillary- bud {k") comes into view 

 in addition to the terminal bud k'. 



