ro Weiss, A Tylodendron-like FossiL 



As Thompson rightly considers that the cone axis 

 often preserves ancestral characters, he believes that the 

 mucilage ducts in the medulla of the latter may repre- 

 sent the " retention of a primitive form of organisation," 

 and it may be that ancestral Araucarineae possessed 

 mucilage ducts in the medulla of their stem. The pres- 

 ence of secretory canals, possibly mucilage ducts in our 

 Tylodendron, might therefore not militate against its 

 identification as a member of the Araucarineae. It 

 must be pointed out, however, that the mucilage ducts of 

 our Tylodendron are far simpler in structure than that 

 figured by Thompson for Arancaria Bidzvellii. The 

 latter is surrounded by a large number of cells, and there 

 has evidently been a considerable meristematic activit}' 

 of the cells surrounding the canal. In the Tylodendron 

 . the canal is normally surrounded b}- 8 to lO large 

 parenchymatous cells of the ordinary type, making up the 

 medulla, and only in one or two cases were new divisions 

 visible in the latter. The canals were therefore of a 

 more primitive type than those of the recent Araucarias 

 described by Thompson. This is, of course, what one 

 might expect in an extinct form. On the other hand the 

 peculiar secretory canal shown in PL II., Fig. 4, with the 

 very numerous divisions of the surrounding cells, shows 

 that the plant already possessed the power of forming a 

 much more elaborate duct not unlike the large mucilage 

 canal figured by Thompson for recent Araucarias. There 

 are, it is true, other differences between the secretory 

 canals of our Tylodendron and the mucilage of recent 

 Araucarias. Those of Tylodendron were never observed 

 to pass out beyond the pith, but it is possible that the\' 

 may do so occasionally, and though tlic)- do not regular!)' 

 anastomose, occasional fusion of two more or less parallel 

 canals seems to have taken place. 



