148 



PART II. THE INTIMATE STRUCTURE OF PLANTS. 



[30. 



stems and roots of most Pteridophyta : for instance, in the stems 



and roots of all 

 Leptosporan- 

 giate Filicinse, 

 and in those of 

 the Ophioglos- 



//J^^/S-VZJ-^A \ \ V\ \ seee (but not in 



those of the 

 Marattiaceaa) ; 

 in those of the 

 Equisetina3 ; 

 and in those of 

 some species of 

 Selaginella (8. 

 Martensii and 

 Kraussiana). 

 The shape of 

 the apical cell 

 is generally a 

 three- sided 

 pyramid with 

 a spherical 

 base, the base 

 being at the 

 surface of the 



member and the apex being directed inwards ; less commonly the 

 apical cell has only two sides or flanks and is then somewhat len- 

 ticular in shape 

 (e.g. that of the 

 rhizome of Pteris 

 aquilina, stem of 

 Salviniacese, and 

 frequently in the 

 above species of 

 Selaginella) . 



In growing- 

 points of this 

 structure it is 

 seen (Fig. 112) 

 that the embry- 

 onic tissue-systems are not continuous as in the Phanerogams, 



FIG. 112. Growing-point of the stem of Equisetum arvense, in 

 longitudinal section; t apical cell; s's" successive segments; 

 p anticlinal segment-wall; m wall dividing the segment into an 

 upper and a lower cell; pr periclinal wall dividing the segment 

 into an inner and an outer cell ; ff'f" successive whorls of leaves ; 

 g initial cell of a lateral bud. (After Strasburger : x 240.) 



FIG. 113. Diagrams illustrating the division of the apical 

 cell of the stem of Equisetum : A longitudinal section ; B sur- 

 face view. The numbers 1-7 indicate the successive segmental 

 walls ; the fainter lines indicate the walls of subsequent divi- 

 sions of th e segments. 



