TH3 TREE ITS SHOOT-SYSTEM. H3 



through which the protoplasmic and other contents of 

 the continuous segments pass uninterruptedly. Similar 

 sieve-plates occur on the lateral walls of the segments 

 also. The walls are not thickened and not lignified, and 

 thus the morphological similarities between the sieve- 

 tubes of the bast and the vessels of the wood (which only 

 contain air and water, have their septa absorbed, and 

 their walls lignified and covered with bordered and sim- 

 ple pits) depend almost entirely on the similar develop- 

 ment. The sieve-pores are very fine, and easily over- 

 looked. 



(3) The bast fibers (Figs. 17 and 18 ), which are 

 homologous with the libriform fibers of the wood, and 

 are developed in the same way from single cells of the 

 cambium. They are short, blunt, very thick-walled 

 fibers, grouped in strands which appear on the trans- 

 verse section of the bast as tangential bands 2-4 deep, 

 alternating (in the radial direction) with broader bands 

 of sieve-tubes and parenchyma. These bands of fibers 

 (hard bast) are accompanied at their outer and inner 

 boundaries by parenchyma-like cells arranged in vertical 

 rows, each of which contains a large simple crystal of 

 calcium oxalate imbedded in yellowish substance, and 

 the walls of which are slightly sclerotic. Similar verti- 

 cal series of cells are found in the soft bast, but they con- 

 tain compound (clustered) crystals of the same salt (Figs. 

 17 and 18, e). 



The soft bast also contains scattered roundish groups 

 of short sclerenchyma cells, the thickened walls of which 



