EQUISETUM SPOROPHYTE 337 



alternate one with another. In the centre of these rings 

 there will be found in each of the lower sections of the 

 series a transverse section of the axis, and one of 

 the sections should include the punctwm vegetationis, 

 which would thus be seen from above. In this pre- 

 paration observe that the apical cell appears of 

 triangular outline (compare Fig. 13), while the seg- 

 ments are arranged regularly around it: from this 

 observation, and from its appearance in the longitudinal 

 section, it may be concluded that the apical cell has the 

 form of a three-sided pyramid, and that segments 

 are cut off from three sides. From the observation of 

 transverse sections cutting the axis below the apical 

 cell, and a comparison of these results with those 

 drawn from a study of longitudinal sections, the mode 

 of subdivision of the segments should be fully made out. 

 X. Cut transverse sections of a well-developed root 

 of E. arvense: treat them with potash, and mount 

 i n glycerine : examine them under a high power, and 

 observe 



1. That there is a peripheral band of tissue with 

 dark brown walls: single superficial cells have grown 

 out as root-hairs. 



2. Then follows a broad band of colourless cortex, 

 with large intercellular spaces : this is limited internally 

 by- 



3. A definite layer of cells having the well-marked 

 characteristics of the endodermis. 



4. Within this is the pericycle, the cells of which 

 are opposite to those of the endodermis, and are 

 derived with the latter from the inmost layer of the 

 cortex. This surrounds 



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