300 PRACTICAL BOTANY 



I. The phloem-sheath, or pericycle, is composed of wider 

 oblong cells, with colourless protoplasic contents : the ends are 

 square or oblique. 



c. The sieve-tubes appear as wide tubes, with pointed ends, 

 and cellulose walls : the surfaces of the walls which separate 

 contiguous sieve-tubes are covered with numerous sieve-plates 

 (best seen in sections treated with chlor-zinc-iodine), to which 

 round, highly refractive granules adhere : the sieve-tubes are in 

 fact essentially similar to those of Aspidmm (p. 297). Note 

 especially the irregular outline of the wall when seen in 

 longitudinal section : this will be best seen in sections which 

 have been cut so as to pass through the phloem in a plane 

 parallel to the flattened side of one of the larger bundles. 



d. The scalariform tracheides, which are the main con- 

 stituents of the xylem : they are similar in all their main 

 characters to those of Aspidiuni (see p. 297), being elongated and 

 pointed, while the walls are marked by transversely-extended 

 bordered pits, arranged regularly so as to give the ladder-like 

 appearance ; but they differ from them in one point, for by 

 a careful examination of fine sections it may be ascertained that 

 the pit-membrane, which remains permanently in Aspidium, is 

 often broken down on the oblique terminal walls in Pteris : this 

 is, however, exceptional for Ferns. 



e. The conjunctive parenchyma, distributed among both 

 sieve-tubes and tracheides. 



X. From around the apical bud of a well-grown 

 plant of the Male Fern remove successively the bases 

 of the leaves of previous years, those of the current 

 year, and finally the larger circinate leaves, which would 

 have unfolded in the following year. Carefully remove 

 the smaller ones with a scalpel, and then with forceps 

 gradually pull off the large mass of brown scales, which 

 completely cover the extreme apex. With a stiff camel's- 

 hair brush remove the bases of these scales, together 

 with the youngest of them, which will still remain 



