a8o 



THIRD GROUP. VASCULAR CRYPTOGAMS. 



at the lower part of the sporogenous tissue, but not at the part where this abuts upon 

 the wall of the sporangium. The spore-mother-cells become isolated and invested with 

 thick walls, and divide into four compartments (' special mother-cells ') within which 

 each of the four protoplasmic bodies becomes invested with its permanent cell-wall ; 

 when the cell-wall has acquired its bosses, spikes, and the like markings, the walls of 

 the compartments of the mother-cells dissolve. 



Histology. The epidermis of the leaves of L. annotimem, L. clavatum, and L. Selago 

 has stomata on both surfaces, and often in small groups ; the heterophyllous species with 

 four rows of leaves have stomata on the whole upper surface of the leaf and on the under 

 surface of the part of the leaf, adhering to the stem, which is turned towards the ground. 

 The epidermis of the root is sometimes strongly cuticularised, as in L. clavatum. 



The cells of \h& fundamental tissue of the stem are sometimes everywhere thin-walled, 

 as in L. inundatum ; usually and especially in the inner layers they are thick-walled 

 and prosenchymatous, or even sclerenchymatous, but never of the brown colour of the 



Ferns (Fig. 228). The fundamental 

 tissue is separated from the axile 

 vascular cylinder by a strongly de- 

 veloped bundle-sheath composed of 

 from one to three layers of cells. 

 Air-cavities occur in the fundamental 

 tissue in the leaves of the hetero- 

 phyllous species, and in the stem 

 also in L. inundatum ; in this species 

 also Hegelmaierfound gum-passages 

 formed by the separation of cells in 

 the stem and leaves (one in the 

 mid-rib) ; the bordering cells have 

 the shape of varicose hairs and pro- 

 ject into the passage ; L. annotinum 

 has similar passages only in the 

 spikes. 



The vascular bitndles of the Lyco- 

 podiaceae are very characteristic, 



and form one large axile strand usually with a circular transverse section in the stem and 

 root. In this strand (Fig. 228) the xylem lies in bands which are either quite separate 

 from one another or unite with one another in various ways, so that the xylem forms 

 figures which are divided into symmetrical halves by an axile longitudinal section. 

 Transverse sections at different heights in a shoot show different arrangements of the 

 xylem, because the bands anastomose in their longitudinal course. These xylem-bands 

 consist, as in the Ferns, of tracheides pointed at both ends and increasing in breadth 

 from without inwards, the narrow ones with roundish pits, the broader with pits that 

 have the form of fissures. Very narrow spiral tracheides occur at the outer edges only 

 of the xylem-bands. The concavity of the bands in creeping and oblique stems is 

 always directed upwards. The bands are inclosed in narrow-celled phloem, in which are 

 rows of broader elements between the xylem-bands ; these elements may be regarded as 

 representing sieve-tubes, though according to Hegelmaier they have no sieve-plates. 

 Between the peripheral corners of the xylem-bands are bast-like fibrous elements, the 

 ' protophloem-elements ; ' thus we have an arrangement which reminds us in many 

 respects of that in the axile cylinder of the roots. The peripheral phloem inside the 

 bundle-sheath is surrounded by some layers of broader cells, which Hegelmaier terms 

 phloem-sheaths, and which may certainly answer to the layer in the Ferns which is so 

 named. The axile cylinder in the stem of the Lycopodiaceae may be considered to be 



FlG. 228. Transverse section of a stem of Lycopodiicm Chaitiaccyparissits. 



