172 



I ) 1 ;s -RTPTI VF. C ATA LO( J I' E 



raoasuroments of the larger elements in his sections, however, 

 give about 90 p as the average for the larger pith-cells, which lie 

 towards the centre. Between their rounded walls are triangular 

 intercellular spaces. A small group of cells forms a medullary 

 sheath round the projecting primary bundles. The pith-cells 

 are all thick-walled and pitted. 



The primary bundles of the wood form small well-marked 

 groups. The protoxylems appear to be spiral. There is 

 no evidence of the existence of centripetal xylem. ,SV,;M ///// 

 wood consists entirely of tracheids and wood-parenchyma. 

 The largest of the spring tracheids measures only about 

 17 X 25 f.t, the majority rather less than this, while the 







a. 



Text-fig. 49. Cnjirc^i/ii'.i'//fu,i > l.arhrr. Knclial views of 



to show pitting, a., pits in a single roxv ; h. t adjacent pits in a single 

 row, which is occasionally doubled. After Barl>er. 



autumn elements averae about 10-11 



Thus the wood is 



seen to be very small-celled. Mr. Barber made large number-; 

 of very minute measurements of the size of these elements 

 (see pp. 345-^348, Barber, 1S98); the systematic importance of 

 the size of the elements, however, is much less than was at one 

 time supposed. The walls, even of the spring wood, are much 

 thickened ; as an average of 80 measurements Mr. Barber gives 

 a range of wall-thickness of from 4 ^ to 14 ^t. The bordered 

 frits in the tracheid- walls are inconspicuous in transverse 

 section, in radial section they lie, as a rule, in a single row, the 



