AEATJCAKIOXrLON. 57 



The wood abuts on the perimedullary zone in the form, of 

 bluntly terminated wedges. The annual rings are very distinct 

 (PI. VI. Fig. 1) ; those on one side of the pith vary in width from 

 1 to 2 mm., while on the other side they reach a breadth of 

 3'5 mm. : this feature bears an interesting resemblance to the 

 inequalities frequently seen in the wood of recent trees which are 

 •due to the more vigorous development of tissue on that side of 

 the stem exposed to the more favourable quarter. In one part of 

 the section there appears to be an indication of a double annual 

 ring, represented by a narrow zone of smaller tracheids in the 

 spring wood. The medullary rays are clearly seen in PI. VI. 

 Pig. 1 as dark bands, and in. Pig. 5, PI. VII. two rays are shown 

 in surface-view ; they consist of radially elongated parenchymatous 

 cells which occasionally exhibit small simple pits, and the cavities 

 are often full of vacuolated brown contents. The rays vary in 

 •depth from one to fourteen rows of cells. 



The wood appears to be without resin-canals, but in one or two 

 places there occurs a series of irregular cavities — as shown at r, 

 Pig. 3, PI. VII., and in longitudinal section in Pig. 2, c, PI. VI. — 

 bounded by dark-brown parenchymatous cells with convex walls 

 bulging into the oval or cii'cular spaces. These spaces are not 

 regular enough to be compared with the resin-canals of the 

 Abietineae, and their occurrence is exceptional and local. In the 

 portion of the stem represented in Pig. 3, PI. VII. , they occur in the 

 spring wood ; in this interrupted series of spaces one is able to trace 

 the development of the irregular cavities from patches of dark-brown 

 cells, which gradually separate to form a space into which resin 

 may have been secreted. Seen in longitudinal section (51,724, 

 PL VI. Pig. 2), the cavities are bounded by one or two rows of 

 short parenchymatous cells, and these short elements are in places 

 separated from the tracheids by a row of long and narrow cells. 

 In aU probability these spaces may be regarded as the result of 

 abnormal conditions, which have caused the formation of a resinous 

 secretion. A similar occurrence of abnormal secretory parenchyma 

 is figured by Conwentz ' in the wood of Pinites preserved in 

 Baltic amber. 



Whitby, Upper Lias. Bryson Coll. 



' Conwentz (90), pis. fi.-viii. 



