52 



during the process, the free end of the original leaf is thrown back and forms 

 the spur on the dorsal surface on each \-alve of the cone, as shown in these 

 figures. The gradation of such processes is complete from Figures 29 to ^^, in 

 which latter only one spur has been dissected. In e\-ery case a number of sub- 

 tending leaves are shown. 



Figures 34 to 37 give a similar series, but taken from a more ad\-anced 

 cone, and show, besides the above features, the complete closing in of the 

 fertilised ovules or zygotes /';/ situ. 



Figures ^j, 38, and 39 are given to show (i) the junction of enlarged portion 

 of the sporophylls at the apex or dome of the cavity, and (2) the spurs nearing 

 their final stages in the cone's life history. These are also interesting as they show 

 the row of oil ca\-ities on the inner and outer surfaces, the former being backed by 

 a row of bundles — marked by dark oval patches. Some also are seen behind the 

 oil caWties below the dorsal surface. 



XIII. PROBABLE FUNCTION OF THE CENTRAL COLUMELLA OF 



THE CONE OF CALLITRIS. 



In all species of this group there is present in the inside at the bottom of the 

 cone a central column, sometimes simple in form when it is pyramidal, and at 

 other times compound or three-lobed, but varying in length in indi\idual 

 species. 



.\s far as our knowledge goes no function has been assigned to this body, 

 nor could any reference be found accounting for its origin except a remark by 

 Bentham, who, in the " Flora Australiensis " (VI, p. 234 , states that " they are 

 sometimes apparently formed of abortive ovules." 



The inference from this statement is that it is not a regular character, but 

 should only be found when abortion occurs, but this is not borne out by facts, as 

 it always occurs in the cones, and may, therefore, be regarded as a persistent 

 character, and is generally of a uniform shape and length in each species, so that if 

 formed by chance, such as fertilisation or non-fertilisation of o\'ules, its occurrence 

 would be occasional, but such is not the case. 



.\natomically, both before and after the dehiscent period of the cone, it is 

 identical in structure with the inner portion or ovule-bearing area of the sporophyll, 

 as well as that of the ovules. In the first of these stages the columella is composed 

 of nucleated, closely packed, irregular parenchymatous, starch-containing cells, 

 which have their origin in the centre of the branchlet from whence they emerge, 

 and form, not only the tissue of the columella, but also the bulk of the substance 

 or structure of the sporophylls, or what are later the six cone valves. 



