4i8 KKkNS LESS. 



small cells, the inner called X\\c phlocm-slwatli or periiyc/e, the 

 outer, the bundle-sheath or endodermis {b. sh). 



The cells of the phloem are for the most part parenchy- 

 matous, but among them are some to which special 

 attention must be drawn. These (n and c, w. /), are many 

 times as long as they are broad, and have on their walls 

 irregular patches or sin<e-p/<ites (f, sv.p/.) composed of groups 

 of minute holes through which the protoplasm of the cell is 

 continuous with that of an adjacent cell. The transverse or 

 oblique partitions between the cells of a longitudinal series 

 are also perforated, so that a row of such cells forms a sieve- 

 tube in which the protoplasm is continuous from end to end. 

 We have here, therefore, as striking an instance of a non- 

 cellular tissue as in the deric epithelium and certain other 

 tissues of Polygordius (see p. 289). 



The distal or growing end of the stem terminates in a blunt 

 apical cone or punctum vegetationis (c), surrounded by the 

 leaves of the terminal bud in the case of vertical stems, or 

 sunk in a depression and protected by close-set hairs in the 

 underground stem of the bracken. A rough longitudinal 

 section shows that, at a short distance from the apical cone, 

 the various tissues of the stem — epidermis, parenchyma, 

 sclerenchyma, and vascular bundles — merge insensibly into 

 a whitish substance, resembling parenchyma to the naked 

 eye, and called apical meristem {ap. mer). 



Thin sections show that the summit of the apical cone is 

 occupied by a wedge-shaped apical cell {ap. c) which in 

 vertical stems is three-sided like that of mosses (Fig. 108, h, 

 p. 401), while in the horizontal stem of Pteris it is two-sided. 

 As in mosses, segmental cells {seg. c) are cut off from the three 

 (or two) sides of the apical cell in succession, and by further 

 division form the apical meristem {ap. mer), which consists 



