19^ 



Figure 12S is interesting as it shows the effect of cutting a section from 

 a dried specimen, the shrinlcing in this case being indicated by the pinched sides 

 below the dorsal ridge. 



The effect of the lateral shrinkage is to compress the oil cavity, and the 

 volatile constituent of the oil having departed, the resinous portion remains and 

 almost fills the compressed ca\ity as a dark spathulate body, in fact, not unlike 

 the ligule figured in some illustrations of Lepidodendron leaves, but, of course, it 

 is not a similar body. If found in a fossil condition, this is most probably what 

 a section would rejirescnt. 



This is also interesting as showing how, in this instance, the transfusion 

 tissue has massed itself around the inner side of the oil cavity. In Figure 129 is 

 seen a transverse section through the upper portion of the three leaves below the 

 free ends, but prepared in a fresh condition in alcohol; three oil reservoirs have 

 been cut through, which are marked by the oval, blank spaces in each leaf, such 

 as would have appeared in Figi:re 128 if the specimen had not been dried. In 

 Figure 130 the edges of the section are not perfect, but it is given, as the whole 

 median tissue is so clearly defined, and gives one a good idea of the evident unity of 

 the physiological functions in the organs of the collaterally placed leaves and median 

 axis, for they must all here act in unison for the plant's welfare, and might be 

 regarded in this respect as one whole leaf. The three dark oval bodies towards 

 the base of the leaves are sclerenchymatous cells, and between these and the 

 phloem of the a.xis of the branchlet is the leaf bundle, and surrounding these are 

 parenchymatous cells ^all empty) and transfusion tissue. Figure 131 well illus- 

 trates how the parenchymatous endodermal cells dispose themselves when oil 

 reser\'oirs are present, and they are here well defined surrounding the central 

 axis and extending nearly to the top of the oil cavities, the secretory cells of which 

 are also well defined in this section. Figure 132 is a 150-magnification of the 

 central axis and the surrounding tissue, and is given to show more clearly the 

 disposition of the organs, which go to make up the latter substance, and which 

 from the previous remarks given under Figures 129-131 should not be difficult 

 to follow. The clusters of sclerenchymatous cells abutting on the phloem of the 

 leaf bundles are well emphasised, and one or two can also be detected 

 in the neighbourhood of the phloem of the main axis. The transfusion cells, 

 marked by single circles (bordered pits i in each, are irregularly scattered amongst 

 the empty parenchymatous cells. The three V-shaped dark figures just coming 

 into the picture are the bases of the decurrent channels. From the above remarks 

 it should not be difficult to follow the structure in Figure 133, which is a 175- 

 enlargement taken in the neighbourhood of the decurrent channel in the top of 

 Figure 131. Figure 134 gives a view of a lonL^dtudinal section through a node 

 showing the free end of one leaf on tlic right and ;in oil cavity in the leaf on the 

 left. 



