1 88 THE ANATOMY OF WOODY PLANTS 



species of Potentilla, namely, P. intermedia. In this instance the 

 same outstanding and depressed segments are found as in the 

 previous species, but the conditions otherwise differ in important 

 respects. The depressed segments corresponding to leaf traces 

 in P. intermedia are represented in solid black, which is the 

 diagrammatic expression of the fact that they are no longer com- 

 posed of fibrous elements, as is the case with the species discussed 

 above. The substance of the segments is now, in fact, entirely 

 parenchymatous, and they are comparable to the compound type 

 of ray found in the oak and similar forms. On the other hand, 

 the fibrous regions of the cylinder in P. palustris supply the equiv- 

 alent of the aggregate rays of the alder and of types which 

 resemble it. In d is shown a more magnified view of a part of c. 

 The cylinder presents three annual rings, which are seen in both 

 outstanding and depressed segments of the stem. In the inner- 

 most annual increment of the depressed foliar region is imbedded 

 the leaf trace, marked by the presence of vessels. Obviously it 

 is not only faced by parenchymatous tissue (indicated in black), 

 but is likewise flanked by the same substance precisely as in b the 

 trace is faced and flanked by the fibrous modification of the wood. 

 In d we have the thick cylinder resulting from perennial growth 

 during several years. If the external region of this cylinder were 

 cut away to such a depth as to reach the surface of the leaf trace, 

 we should have the condition which is found in an annual stem of the 

 same plant, such indeed as is shown in e. The topographical con- 

 sequence of the thinning out of the woody cylinder, as a result both 

 of less massive development and of the annual habit, is the increas- 

 ing of the relative importance of the leaf traces as components of 

 the woody cylinder. This means that the storage cells which 

 originally not only flanked but also subtended the traces are now 

 confined to the sides or flanks of the foliar traces and, in fact, 

 separate these from the adjacent segments of the cylinder. This 

 situation is distinctly shown in e for the cylinder as a whole, and on 

 an enlarged scale for a single foliar trace and the two adjacent 

 segments of the woody cylinder in /. It is clear from the diagram 

 supplied in Fig. 140, which may be profitably compared with that 

 illustrating the topographical and evolutionary features of the 



