OF LOWER GHEESSAND PLANTS. (>.'i 



in the quantity of resinous xylem parenchyma ; and in the 

 proportion of ray parenchyma to tracheids in a given bulk of 

 wood. 



Even the presence or absence of ray-tracheids is a less 

 constant feature than was recently supposed, as they have been 

 found in Cunn.inyhamia (see Jeffrej', 1908), Sequoia (see Gordon, 

 1912), etc. This being the case, it may well be asked whether 

 there is any possibility of determining fossil woods at all and 

 the answer is in the affirmative. Gothan especially has directed 

 attention to a very important and relatively constant feature 

 of woods, viz. the pitting of the radial and end walls of the 

 medullary ray-cells. While the details may vary a little, the 

 type of pitting here is remarkably constant in a species. Before 

 accepting his conclusions, I worked over a very large number of 

 both fossil and recent woods, and, as a result, can, in the main, 

 confirm his position when he bases species and even genera on 

 the ray-pitting. Though I must note that the " abietinean 

 pitting " is not an absolute criterion of Abietinean affinity, 

 since I have found that it is present in Juniperus dentalis and 

 J. paclnjitliloza, for instance; nevertheless, the radial pitting of 

 the ray-cells is remarkably constant and is extremely valuable 

 for separating species, for it may differ considerably and 

 constantly in two species so alike in other respects of their 

 anatomy as to be inseparable except from their external 

 characters. 



The leading features, which, when taken together, give 

 enough data on which to base fairly reliable determinations 

 are the following : the presence or entire absence of growth- 

 rings ; the presence or absence of normal resin-canals in both 

 vertical and horizontal directions, and if they are present the 

 thin-walled, or thick and pitted nature of their epithelium ; 

 the presence and position of traumatic resin-canals ; the presence 

 or entire absence of resinous or other wood parenchyma ; the 

 presence or absence of tangential pits in the tracheids (the 

 arrangement of the round bordered pits or absence of Sanio's 

 bars is of secondary value); the presence of hexagonal-bordered 

 pits in two or more rows in the radial walls of the tracheids ; 

 the uniseriate or multiseriato nature of the medullary rays; 

 the thickening and pitting of the end walls and lateral walls 



