298 PRACTICAL BOTANY 



numerous sieve-plates (best seen in sections treated 

 with chlor-zinc-iodine), to which round, highly refractive 

 granules adhere: these stain yellow with chlor-zinc- 

 iodine. Note also the irregular beaded appearance of 

 the walls when seen in longitudinal section. 



1}. Cells of the conjunctive parenchyma, inter- 

 spersed among the sieve-tubes. 



As the vascular bundles of the rhizome of Pteris (the common 

 Bracken) are more regularly typical of the concentric bundle of 

 the Fern, than those of Aspidium, thin transverse sections should 

 also be prepared from the rhizome of this plant, or the rhizome of 

 Pteris may be taken as a substitute for the stock of Aspidium ; 

 mount some of the sections in glycerine, others in chlor-zinc- 

 iodine ; or these sections may be stained with hsematoxylin and 

 mounted in Canada balsam (p. 52). 



First examine the whole section under a low power, and note 

 its oval form, the upper and lower surfaces being flattened. It 

 is composed of the following tissues : 



1. A peripheral band of brown sclerenchyma, outside which 

 is a scarcely distinguishable epidermis. 



2. Colourless, iparenchymatous ground-tissue, in which are 

 embedded successively the following : 



3. An outer series of relatively small, sharply circumscribed 

 vascular bundles, arranged in an irregular ring : one larger 

 bundle is usually to be found opposite the lower flattened 

 surface. 



4. An incomplete ring of dark brown sclerenchyma, com- 

 posed of two parts which are usually distinct, viz. an upper 

 strongly curved portion, and smaller flat portion which is nearer 

 the lower surface : small isolated patches of brown sclerenchyma 

 may also be seen dotted about in the ground-tissue. 



5. A central series of bundles, usually two or three in 

 number, and of larger size : they may sometimes be found to be 

 connected at their margin into one irregular ring-like mass. 



Examine the sclerenchyma under a high power, and note the 



