ANATOMY OF lildd 11 1! gto Ilia AND C'alliti'is. 



285 



the tannin (?) containing tracheids is also shown. It 

 may be pointed out that in a z'cry thin median section of a 

 bordered pit the thickenings are not seen to extend round the 

 cell, but appear only as horns projecting" into the cavity of the 

 tracheid from the upper and lower margins of the bordered pit. 



The metaxylem of Callitris robusta only differs from that of 

 C. verrucosa in the fact that the contents of the secretory 

 tracheids are much less dense than is the case in that species.'* 

 In all other respects the structure seems identical. 



In IViddriiigtoiiia cuprcssoidcs the structure of the wood is 

 decidedly different from that of CalUfris. A few secretory cells 

 are met with, but they are scattered throughout the thickness 

 of the wood, and not aggregated to form concentric rings. In 

 tangential section the bordered pits are seen to be smaller than 

 those of Callitris, and no trace of thickenings, extending from 

 their margins, is found. \'ery rarely traces of spiral thicken- 

 ing are found in the metaxylem. but not in relation to the pits. 

 In some tracheids, however, a considerable number of obliquely 

 elongated bordered pits are seen on the tangential w'alls. These 

 are very slightly smaller than the circular pits, and may occur 

 in either one or two rows. The various points mentioned are 

 indicated in Figure jo. 



Fig. 10. 



Fig. 1 1. 



Fig. 10. Part of a tangential section of the wood of Widdringtonia cuprcs- 

 soidcs. M = Medullary ray. ( x 4 1 5 . ) 

 ,, II. Part of a transverse section through the cambium and inner phloem 

 of Callitris robusta. Cellulose walls black or deeply shaded : 

 Lignilied walls of bast fibres lightly shaded. M = Medullary 

 ray. (X270.) 



In all three species the structure of the phloem is the same. 

 It consists of alternating concentric bands of hard and soft 



* It is possible that this difference is wholly or partly due to the fact 

 that the wood of C. verrucosa had been hardening in alcohol for some 

 months, and that of C. robusta for only two days, when cut. The difference 

 might also be due to the fact that they were collected at different seasons, 

 C. verrucosa in summer, C. robusta in winter. 



