ASPIDIUM SPOROPHYTE 293 



it is better therefore to cut a number of sections, each 

 extending over a comparatively small area, and to 

 study the various tissues separately. Mount some in 

 glycerine or glycerine jelly, others in chlor-zinc-iodine. 

 Examine under a low power, and observe successively 

 the following tissues, starting from the periphery of the 

 stern : 



a. An epidermis, consisting of a single, somewhat 

 irregular and ill-defined layer of cells, with dark brown 

 outer walls : their arrangement is disturbed at the point 

 of insertion of the scaly hairs which appear as plates 

 of cells, one layer of cells in thickness, rising obliquely 

 from the epidermis. Beneath this is 



1}. The ground-tissue, which is differentiated as 



i. An outer narrow band of tissue, with rather thick, 

 colourless, pitted walls, and cell-contents with much 

 starch : there are no intercellular spaces. 



ii. A band of sclerenchyma with thick, yellow, 

 lignified, obviously stratified, and pitted walls, 

 cell-contents as in (i.), and no intercellular spaces. 

 This merges gradually into 



iii. The bulky central mass of ground-tissue, in 

 which the vascular bundles are embedded. It con- 

 sists of cells with comparatively thin, pitted, cellulose 

 walls, protoplasmic contents with much starch, and with 

 intercellular spaces. 



On the external surface of those parts of the cell-walls which 

 adjoin the intercellular spaces numerous small projecting spikes 

 may be observed : it may be readily seen that these originate in 

 connection with the formation of the intercellular spaces. 



Internal glandular hairs are also found in the intercellular 

 spaces : they are attached by narrow stalks to single cells of the 



