526 MOSSES AND FERNS chap 



If we examine a longitudinal section of the stem a short 

 distance below the apex (Fig. 303, A), we find a regular inter- 

 cellular space formed between the central stele (or steles), 

 which completely surrounds it, and becomes very conspic- 

 uous as the section is examined lower down. The formation 

 of this lacuna is similar to that in the capsule of the Bryales, 

 and, as there, the central mass of tissue is connected by 

 TOWS of cells with the outer tissue. These rows of cells (tra- 

 beculse) are at first composed of but a single cell, but later by 

 tangential walls become slender filaments by which the vascu- 

 lar cylinders are suspended in the large lacuna which occupies 

 the centre of the stem (Fig. 304, t). According to Stras- 

 burger ((7), p. 457) both the trabeculse, which are usually re- 

 garded as endodermal, and the pericycle, are of cortical origin. 



The fully-developed bundle in .S". Kraussiana (Fig. 304, B) 

 shows a pericycle composed of a single la^er of rather large 

 cells, within which lies the phloem, which completely surrounds 

 the xylem, as in the Ferns. The sieve-tubes in this species 

 form a single circle just inside the pericycle, but according to 

 Gibson ( (2), p. 176) are absent opposite the protoxylem. He 

 states that there is but a single group of protoxylem elements 

 here, but my own observations lead me to think that there are 

 two, as Russow affirms is the case. The origin of the proto- 

 xylem was not traced, but the appearance of the mature bundle 

 in the specimens examined (Fig. 304, B) points to this con- 

 clusion. The protoxylem is made up of small spiral and an- 

 nular tracheids, the metaxylem (secondary wood) of larger 

 scalariform elements, as in Lycopodium. The sieve-tubes 

 have delicate walls and numerous, but poorly developed, sieve- 

 plates upon their lateral walls. 



While in the main the anatomical characters are essentially 

 the same in all species examined, there are a number of differ- 

 ences to be noted (Gibson (i, 2)). Thus the stem may be 

 monostelic (S. Martensii), bistelic {S. Kraussiana), polystelic 

 {S. IcBvigata). In the former species the presence of silica in 

 the inner cortex has been demonstrated by Strasburger, and 

 Gibson has shown the same thing in other species. In this 

 species, too, besides the simple trabeculae found in S. Kraus- 

 siana, others occur in which the outer cells undergo divisions in 

 more than one plane, and form a group of cells with which the 

 endodermal cell is articulated. In all species examined these 



