294 



PRIMARY ARRANGEMENT OF TISSUES, 



But in this case there is this further peculiarity, that from the upper part of each 

 lateral margin of a foliar gap two or several bundles arise, which unite after a short 

 course into one, and that these bundles from their point of origin onwards are sur- 

 rounded by a thick sheath of sclerenchyma. Together with the latter they form on 

 each side of the foliar gap a cone several millimetres thick at the point of origin ;, 

 they either taper to a point towards the adjoining lower gaps, and end blindly in the 

 parenchyma, or coalesce with the margin of the adjoining lower gaps, and with a 

 cone which there arises. The sclerenchymatous sheath of the cone shows slits here 



and there, through which unsheathed 

 branch bundles emerge and turn down- 

 wards. Cones, fundamentally similar 

 to those described, the points of which 

 end blindly in the cortex, and indi- 

 cate with certainty the presence of a 

 system of cortical bundles similar to 

 that in C. Imrayana, were first found 

 by Mettenius ' in a dry stem of Also- 

 phila Haenkei. In other species a 

 system of cortical bundles is un-. 

 known, partly because of the difficulty, 

 of finding it in dry stems subjected 

 to investigation ; in many species 

 however (for instance Cyathea arborea 

 and Alsophila microphylla may be 

 named with certainty) it is altogether 

 absent. 



Sect. 86. Most species of Denn- 

 simdlia have, as above indicated, a 

 simple tube of bundles which is closed 

 , with the exception of the narrow foliar 

 gaps. Within this, and near the upper 

 side in the horizontal stem, there are 

 in the pith of D. rubiginosa one, in D. 

 cornuta several small bundles with 

 circular transverse section, in D. cornuta these form a tube alternately closed and 

 again split into 2-3 bundles. At the base of a shoot the medullary bundles arise 

 from the inner surface of the tube, at the foliar gap they approach the latter, and 

 divide into a few branches, of which some anastomose with the margin of the gap, 

 others enter the leaf with those which start from the gap, the third series (or single 

 bundle) ascending further in the shoot as medullary bundles ^■ 



The somewhat more complicated arrangement in Chrysodium vulgare, on 

 which compare Mettenius, I.e., may be placed in connection with the above. 



Fig. 142.— Cyathea Imrayana; piece of a living stem witll 

 four bases of petioles, the outer layers of cortex being peeled 

 off; seen from without. The margins of four foliar gaps, tjle 

 bundles which arise from them and pass into the leaves, with 

 the young roots (black) seated upon them, and the bundles 

 which descend through the cortex, are exposed ; the latter 

 and the roots are quite free, the rest covered by a little trans- 

 parent parenchyma, through whiph they are clearly seen, and 

 all the parts are held together in their natural position. Natural 

 size. 



' Angiopteris, p. 528, Taf. V. A good figure of a transverse section of a Fern stem with cortical- 

 bundles is given by C. H. Schnltz, Mem. present, de I'Acad. des Sciences, torn. VII (1841), pi. 22. 

 ^ Mettenius, Angiopteris, p. 540. 



