88 JOURNAL OF THE [J uly 



around from the outer bast in a clearly marked line to the outer 

 periphery of the included bast. But one explanation can account 

 for this, namely, that the new zone of growth arises in the peri- 

 blem near the cortical sheath. Here, moreover, are all the ele- 

 ments necessary for growth — a living parenchyma rich in chloro- 

 phyll, starch, and protein matter. Only in a single stem was this 

 growth seen to be in process. In this case the cambium seems to 

 have risen on a line with the cortical sheath, for the wood fibres 

 were interrupted by the bundles of sclerenchyma. This may be 

 the place of new growth, since in removing the inner cortex from 

 the wood the line of separation is always dentate, which outline 

 the sclerotic bundled crowding into the wood tissue would exactly 

 produce. It is not always apparent, however, that the dentation 

 is due to this mode of development. The cause of the anoma- 

 lous growth is doubtless due to pressure. As the annual zones 

 are pushed out greater and greater resistance is offered to radial 

 extension by the bast. The sinuous course, in the older stems, of 

 the medullary ray would be indicative of this, but it is to be 

 noted that the irregularity is almost entirely confined to the cor- 

 rugated, gnarled stems and therefore is in great measure due to 

 torsion. The radial distortion of the parenchyma and the col- 

 lapse of the sieve tubes indicate more strongly the pressure of 

 growth. Finally, as regards the fact that the secondary growths 

 are less than those of the primary, it may be held that the plant 

 reaches its maturity at about the twelfth year. Now the potential 

 of the plant life is lower, new elements are added with less vigor, 

 and consequently it can force back the bast for a shorter period. 

 Reviewing the elements of the stem, one cannot fail to be 

 impressed with the wonderful regularity, economy, and fit- 

 ness manifested in the arrangement of the tissue. The xylem, 

 phloem, and periblem each receives its proportional annual in- 

 crease, developing all its parts with a precision truly wonderful. 

 The tough strands of the sclerenchyma were needed at first to 

 give a strong rope of support to the vine with its heavy foliage ; 

 but with the advance of age the complement of this was 

 needed, lightness as well as increased facilities for the trans- 

 mission of food. Now appear the larger elements — the tracheae, 

 hollow cylinders of support, made more light by their sculptured 

 walls, while the tracheids with their thickened walls afford a 



