Macrozamia heteroinera, Moore. 5 



of the stem. I have not been able to follow any girdle for more 

 than about 2 cms., as they all seem to be cut off by periderm for- 

 mation. We may recall the case of Dioon edule, in which Mettenius 1 

 figures the girdles lying very close to the surface of the stem ; 

 also that of the two stems of Stangeria paradoxa described by 

 Solms-Laubach 2 , one of which shewed no leaf-trace girdles, so 

 that he was at first inclined to think that the plant possessed 

 the simple leaf-traces with which we are familiar in Bennettiteae, 

 but the second specimen shewed a normal development of the 

 girdles. He ascribes the loss of the girdles in the first example 

 to bark formation. Worsdell 3 has examined an adult plant of 

 the same species and finds that in this, "No girdle-leaf- trace 

 bundles are seen, although these may have existed at an earlier 

 stage of the plant's life and been subsequently cut off by the 

 advancing periderm." 



(v) The Mucilage Canals. 



One of the most striking features in the cortex and pith of 

 the plant is the abundance of the large branched mucilage canals 

 so characteristic of Cycads. In the young cortex narrow bands of 

 crushed tissue occur between the mucilage canals. This gives an 

 appearance recalling that of the " Augenstructur" of crushed 

 rocks, in which the uncrushed fragments assume an eye-like form 

 with their long axis perpendicular to the direction of maximum 

 pressure. Each canal with the layers of parenchyma immediately 

 surrounding it appears to have increased in size, and the result 

 has been a zone of crushing along the neutral line where the 

 territories of two adjacent canals meet. 



The extraordinary abundance of mucilage in the stem seems 

 to have been a feature common to recent and fossil Cycadean 

 plants. Carruthers 4 , describing a Mesozoic genus, says, " From 

 the absence of structure in all the specimens yet discovered of 

 Bucklandia there is no evidence as to the presence of canals for 

 the secretion of the mucilaginous juice which is so abundant in 

 the living Cycadeae. But our specimen of B. anomala preserves 

 on its surface the casts of large drops of this substance, that had 

 exuded and hardened, so as to mould the rock around them ; and 

 so rich was this fossil in the gum, that, in this specimen, the 

 interspaces between the scales are filled up with it." Vetters 5 , in 

 1884, suggested that the gum canals serve as water reservoirs, 

 their secretions sucking up the excess of water in the rainy season, 



1 Loc. cit. Taf. in. 1. 



2 Bot. Zeit. 1890, p. 180. 



3 Journ. Linn. Soc. Vol. xxxiii. 1898, p. 452. 



4 Trans. Linn. Soc. Vol. xxvi. 1870, p. 685. 



5 Die Blattstiele der Cycadeen, Leipzig, 1884, p. 11. 



