THE HIGHER, CRYPTOGAMIA. 369 



remarkable phenomenon, however, is that exhibited by 

 Isoefes Hj/striv, and Durieui, in the lignification of the 

 masses of cellular tissue of the bases of their leaves,* which 

 varies in the different varieties of these species. The 

 cells remain in the closest connexion, and are thickened in 

 a porous manner by the superposition of dark-brown layers 

 upon the inner walls, so that, as in Niphobolus chinensis; a 

 stony, closed bark is formed round the stem. By the 

 development of new leaves the lignified portions of the 

 bases of the leaves are pushed more and more outwards 

 and — after the death of the herbaceous parts of the leaves — 

 fonn a close spiny covering to the stem which can hardly 

 be cut with the sharpest knife, and is a sad hindrance in 

 the examination of these parts. 



In the three -furro wed species of Isoetes, the end of the 

 stem, which occupies the base of the deep and steep depres- 

 sion of the top of the stem, is a wart of cellular tissue of 

 a much flatter form than in Isoetes lacustris. It grows 

 like that of /. lacustris, by continually repeated division 

 of the single apical cell. The nature of the cell-multiplica- 

 tion is, however, essentially different. The septa, an end- 

 less series of which appear in the apical cell, are turned 

 in three different directions. The apical cell has the form 

 of a three- sided pyramid, with the top turned downwards ; 

 the cells of the second degree are produced by the forma- 

 tion of septa successively parallel to each one of the lateral 

 surfaces (PL LIII, fig. 22). The cells of the second 

 degree form a spiral, winding round the middle point of 

 the primary cell, which spiral, as far as observations have 

 hitherto gone, is always a right-handed one, and becomes a 

 snail- shell- spiral, in consequence of the fact, that the cells 

 of the second degree from the time of their formation 

 grow by expansion and multiplication in all three direc- 

 tions. 



As far as observations have hitherto gone, all the septa 

 formed in the apical cell and turned in one of the 

 three directions, are at right angles to a plane passing 

 through that indentatipn of the stem which is nearest 

 to them. Consequently, in one of the most essential 



* A. Braun, 1. c, pp. 35, 36. 



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