284 



ANATOMY OF Ji' id d r'lii gtoiiio AND CoUitris. 



The transfusion cells are considerably larger than those of 

 C. verrucosa, and bordered pits can nearly always be recog- 

 nised. The thickenings of the wall are relatively smaller than 

 in that species, and in some cases are absent. These points 

 are indicated in Figure 5. 



A part of a section of a leaf of IViddringtouia cuprcssoidcs 

 is shown in Figure 6. The most obvious difference between 

 this and CaJUtris is in the entire absence of a hypoderm, the 

 palisade being found immediately below the epidermis. The 

 larger size of the palisade cells may also be noted, and the fact 

 that a second layer is also present, but less regular than the 

 outer, and with certain of its cells modified as tannin sacs. 

 Another difference is in the transfusion cells, in which no 

 irregular thickenings are found, only bordered pits, as shown 

 in Figure 7. The position of the stomata is essentially the 

 same as in CaJUtris robust a. but only a small number are found 

 in the angles between the leaves. The cuticle is also thinner 

 than in the last-named species. Resin cavities are present in all 

 leaves of Callitris and Widdringtonia but have not been figured 

 here. 



(ii.) Stem. — The structure of the wood of Callitris verrucosa 

 as seen in transverse section is shown in Figure 8. The most 



Fig. 7. 



Fig. 8. 



Fig. 



Transfusion tracheids, Widdringtonia cnpressoides. (X415.) 

 „ 8. Part of a transverse section of the wood of Callitris verrucosa. M = 

 Medullary ray. (Bordered pits are omitted in this figure.) ( x 240.) 



conspicuous feature of the section is the appearance of roughly 

 concentric rings of modified tracheids, the walls of which re- 

 main unthickened, while their cavities become filled with a 

 dense secretion of tannin (?). 



An examination of tangential sections reveals a striking" 

 peculiarity in the method of thickening of the tracheids of the 

 metaxylem. As far as the writer is aware the 

 only Conifer which is known to possess thicken- 

 ings other than bordered pits on the walls of the 

 metaxylem tracheids is Taxiis, in which con- 

 spicuous spiral thickenings are found in addition 

 M^\L ^ to, but independent of, the bordered pits. In 

 Callitris thickenings are found which originate 

 just above and below each bordered pit, and can 

 be traced transversely round the tracheid as far 

 as the opposite wall. This is indicated 

 in Figure 9, in which a part of one of 

 Fig. 9. Part oi a ta.ngentia\ section oi the -wood oi Callitris veryucosa. (X415.) 



