116 



ring which occur at each node. It becomes therefore a matter 

 of much interest to see whether any similar, even though less 

 marked tendency to turn inwards at the nodes exists on the 

 part of the cambium of /. ovalis; and here a slight but striking 

 difference in structure is to be found. In /. tomentella the 

 openings o o PI. XVIII Fig. 4 are at first filled with primary 

 parenchyma-cells which, retaining their soft-walled character, 

 remain capable of division, and can thus take on a cambial 

 activity. In /. ovalis on the other hand these openings are 

 filled with thick-walled cells PI. XIX Fig. 5 Ip Ip which having 

 lost their parenchymatous nature and being no longer capable 

 of division can not furnish a path for the extension of the 

 cambium inwards toward the pith. The investigation of young 

 nodes shows furthermore that this lignification of the tissue 

 Ip takes place at an early stage in the development of the 

 stem, in fact shortly after secondary thickening has begun, 

 while in /. tomentella the normal cambium does not extend 

 itself inwards until the growth in thickness has already pro- 

 gressed much further. It is thus evident that at a time cor- 

 responding to that at which the anomalous cambiums arise in 

 /. tomentella, there exist in /. ovalis no such parenchymatous 

 communications between the pith and cortex as those, which 

 in the related plant occur at every node and permit , as above 

 described, the extension of the cambial activity to the medul- 

 lary tissue. It naturally becomes a matter of interesting spe- 

 culation , what developmental significance these anatomical 

 differences may have for plants, which in other respects are 

 so much alike. But, especially in the absence of comparative 

 biological and physiological observations , it is quite impossible 

 to draw any conclusions on this point. 



Natiatum herpetic um Ham. 



resembles in the principal features of its stem-structure 

 lodes ovalis very closely. It possesses a similar though very 

 narrow ring of first formed secondary wood of characteristic 



