■STRUCTURE OF COLLATERAL BUNDLES. 



335 



and are to be described below in Sect. 112. They also occur on the right-hand side of 

 the figure, and may be known by their notched outline, p parenchyma of the meso- 

 phyll, with an indication of the small crystals of Calcium oxalate imbedded in the walls. 



Sect. 102. The bundles of the leaves of Cycadese and Isoetes, with which 

 perhaps those of Phylloglossum agree, are different from the typical, simply collateral 

 bundles in the arrangement and development of their parts. 





FIG. 157. 



The peculiarity of these bundles, expressed generally, consists in the fact that 

 the essential elements of the xylem are reversed in position and order of develop- 

 ment, as compared with those in the typical cases. In the plants first named there 

 are the additional peculiarities that tracheides appear at a later stage on the border 

 of the phloem, and that the bundles are in many cases united in pairs. 



The bundles of the leaf-trace of the Cycadeae begin in the stem, according to Met- 

 tenius\ as simple collateral bundles, and run out in the same form into the sheathing 

 bases of the leaves, but before entering the petiole of the foliage-leaves, or the apex of 



' Abhandl. d. K. Sachs, Gesellsch. d. Wissensch. VII. p. 573. 



