COURSE OF THE BUNDLES IN THE STEM. 



293 



According as they follow the first or the second course, the sclerenchymatous sheaths 

 themselves form either a tough net traversing the whole pith, as e. g. in the case of 

 a stem which is before me under the name of Cyathea ebenina, or they pass from 

 each leaf inwards and downwards as a sheaf of bundles, with blind and pointed ends, 

 which show frequent anastomoses one with another, but only fewer or quite solitary 

 anastomoses with the sheaves of bundles belonging to other leaves : e. g. Cyathea 

 arborea, Hemitelia capensis (Mettenius), 

 C. Imrayana, and most other species; 

 in Alsophila microphylla and villosa the 

 vascular bundles in the pith are only 

 accompanied by isolated spindle-shaped 

 bundles of sclerenchyma, which are not 

 connected into sheaths till the foliar gap 

 is reached (INIettenius). In most of the 

 dried stems, when subjected to investi- 

 gation, the delicate unsheathed parts of 

 the vascular bundles cannot usually be 

 seen, the tough sclerenchymatous bands 

 alone being clearly preserved. Since, as 

 above stated, the course of these bands 

 is a copy of that of the vascular bundles, 

 the description given for the latter Will 

 suffice also for them. 



Many but not all species have, 

 besides the medullary bundles, acces- 

 sory cortical bundles also. In C. Im- 

 rayana (Fig. 142) these arise from 

 bundles which pass into the leaves, and 

 close above their point of departure 

 from the foliar gap, and in fact from 

 most, but not from all those which 

 branch off from the lateral and lower margin of the gap. They descend with 

 a steep curve from their point of origin into the parenchyma of the cortex; 

 some of them, after pursuing an individual course for a short distance, unite 

 each with another coming from the same foliar gap ; most of them however pass 

 almost straight downwards in the middle of the cortex, and in the neighbourhood 

 of the adjoining lower foliar gaps they either affix themselves at an acute angle on 

 bundles which there arise, or they end blindly. The cortex is accordingly tra- 

 versed by a network of bundles with elongated meshes, which are sometimes 

 quite closed, sometimes open on one side. In the stems in question the cortical 

 bundles, of the thickness of a bristle, usually have no sclerenchymatous sheath; some 

 few, especially those which arise from the upper part of the lateral margin of the 

 gap, are however often accompanied for about i^m from their point of origin by 

 such a sheath, in the form of a channel, which is open outwards ; comp. Fig. 142. In 

 a dry strong stem, bearing the name C. Imrayana (not the same used for the accom- 

 panying figures), a structure similar to .that just described can still be clearly seen. 



Fig. 141. — Cyathea Imrayana: transverse section through 

 the living stem ; natural size ; seen from above. At b, c, d, 

 foliar gaps. All quite black bands and points are transverse 

 sections of sclerenchyma ; all the paler ones are vascular 

 bundles. In and near the foliar gaps, especially a and b, are 

 root-bundles going to the periphery ; y channels at the base 

 of the leaf; a vascular bundles of the main tube; s outer, 

 j' inner plates of its sclerenchymatous sheath. Inwards 

 from s' the pith with its bundles ; outwards from s the 

 cortex with its bundles. 



