SELAGINELLA. SPOROPHORE. 165 



3. The Lacunar tissue, consisting of thin-walled 

 cells, which form irregular trabeculae traversing the 

 intercellular cavity in a radial direction : the inmost 

 cells of these trabeculae have a peculiar equatorial 

 constriction. 



This lacunar tissue is more typically represented in some of 

 the larger species, e.g. S. incequalifolia, S. Willdoncvii, &c. It 

 may be regarded as the equivalent of the bundle-sheath, of most 

 other vascular Cryptogams. 



4. By means of these . trabeculse the single central 

 Vascular bundle is suspended in the middle of the 

 large air-cavity : the bundle is built upon the 

 concentric type, and is composed of the following 

 tissues : 



a. The Phloem-sheath, an irregular band of com- 

 paratively large, thin-walled cells, which completely 

 surround the central tissues, and abut externally on 

 the intercellular cavity, and the trabeculse. 



N.B. The cells of this layer, in common with all the 

 outer tissues, including the epidermis, may contain 

 chlorophyll granules, which are large, and only few are 

 to be found in each cell. 



I. The Phloem, recognised as a tissue with thin 

 cellulose walls, small cavities, and sparing protoplasmic 

 contents ; it forms a continuous band surrounding 



c. The central Xylem, which appears as a spindle- 

 shaped mass of tissue when seen in transverse section, 

 and consists of elements with lignified walls, and no 

 cell-contents. 



N.B. Small vascular bundles of rounded outline, as 

 seen in the transverse section, may be found opposite or 



