154 PRACTICAL BOTANY 



4. The lacunar tissue, the cells of which are elongated in a 

 radial direction. 



5. The pericycie, consisting of elongated parenchymatous 

 cells, with cellulose walls, and often containing chlorophyll. 



6. The phloem, the most prominent elements of which are 

 long narrow elements with cellulose walls and sparing con- 

 tents : these are regarded as the representatives of the sieve- 

 tubes. 



7. The xyiem, the most prominent elements of which are 

 spiral and scalariform tracheides, similar to those to be 

 described below as composing the xylem of the bundle in the 

 Ferns. 



Observe the general arrangement of the stem, leaves, and 

 ligules. 



In the lower part of the sections a mature sporangium may 

 be found in the axil of each leaf. The sporangium may have 

 lost its spores partially or entirely during the preparation of the 

 sections. It will consist of 



a. A short massive stalk. 



b. A wail inclosing the central cavity : the wall will be found 

 under a high power to consist of three layers of cells 



i. The outer consisting of thick-walled cells, more or less 

 elongated radially. 



ii. A layer of small, compressed cells. 



iii. A layer of thin-walled cells, elongated radially : this is 

 the tapetum, which is here persistent until the spores are ripe. 



Surrounded by the wall will be found 



c. Spores of two sorts, contained in different sporangia 



i. Microspores of relatively small size : these will be found 

 in large numbers in certain sporangia, which will accordingly 

 be recognized as microsporangia. When ripe they may be still 

 seen to cohere in groups of four : each spore is a single cell 

 with a brown wall. 



ii. Macrospores of relatively large size : four only of these 

 will be found inclosed in a single sporangium, which is accord- 

 ingly termed a macrosporangium. Each spore consists of a 

 thick wall, with numerous external projections, surrounding a 

 large cavity filled with protoplasm, &c. 



