io8 



CELLULAR CONSTRUCTION 



[CH. 



one of which runs radially inwards through each segment, and finally 

 curving before it reaches the centre inserts itself laterally on one of the 



Fig. I02. A—C, basipetal series of transverse sections of the root-tip oi Dennstaedtiapiinctilobula, 

 after Conard (x20o). A traverses the root-cap showing centrally a recent segment divided into 

 quarters and further subdivided ; B shows the initial cell and three rows of segments separated by 

 the principal walls/,/; C traverses the body of the root at a lower level and shows the principal 

 walls p,p and sextant walls s, s. Tiie initial cell and the second series of 'segments are dotted in B 

 to bring them into prominence. 



principal walls. Many other minor cleavages occur, but these principal and 

 sextant walls are important 

 for the argument that is to be 

 developed later (Fig. 102, C). 

 Lastly, a section transversely 

 through the region of the root- 

 cap, just above the apical cell, 

 shows the method of cross- 

 wise cleavage of the segments 

 from the base of the conical 

 initial cell which go to form 

 the root-cap (Fig. 102, A). A 

 median longitudinal section 

 through a Fern-root is shown 

 diagrammatically in Fig. 103, 

 for comparison with these 

 transverse sections, while it 

 also illustrates the details of 

 tissue-generation which are 

 described in most of the larger 

 text-books. 



In the Leptosporangiate 



Fprnc; parh leaf arises from a ^ig. 103. Diagrammatic median section of the root-tip of a 



rerns cacil leai aii^Cb iium ct Fern, showing the origin of the various tissues m relation 



single superficial cell of the to the initial segmentation. j9= subdivision of a single 



. . segment of the body of the root. C = subdivision of a 



axis, and m some cases a gi^gig segment of the root-cap. (After Conard.) 



