39 



XL THE CONE VALVES. 



The structure of the valves composing the cone has not occupied much 

 attention in the field of research in the past ; and^ although apparently simple 

 enough organs in themselves, yet, their true relative position in the plant's life 

 history has remained in a measure an unsolved problem. 



Working in this remote part of the world great difficulty has been experienced 

 in obtaining access to the cognate literature, but in all the works examined little 

 or no reference could be found bearing on the origin of the cone scales or valves 

 of our Australian CallUris. 



These organs may be divided into two periods of life history, viz.: — her- 

 baceous and indurated. During the first of these conditions they have all the 

 characters of the ordinary leaf of the genus, i.e., the mesophyll with its palisade 

 parenchyma and spongy tissue, parenchymatous cells, together with a primary 

 bundle, oil cavities, assimilatory and transpiratory surfaces, — structures which make 

 them practically, to all intents and purposes, leaves of two terminal whorls. 

 Starting life thus with all the morphological, functional, and anatomical characters 

 of a leaf, the period of their metamorphosis into sphorophylls is marked structurally 

 by a numerous subdivision of the bundles of the central axis and the pith cells 

 or tissue, and these branches at once ramifying at first into the upper portion 

 of the leaf, but eventually push back and replace the parenchymatous cells and 

 spongy tissue. These bodies or cells as they emerge from the stele are found to 

 be well charged with starch grains, and especially so as the sporophyll becomes 

 almost entirely composed of cells similar to those which are in direct com- 

 munication with the ovules, whose whole structure is also formed of them. 

 Whilst this cell development is taking place, numerous bundles are ramifying 

 through the sporophyll structure generally, at first, in a row just below the inner 

 surface, from which are sent "branches in the dorsal direction. Oil cavities are 

 also formed both at the inner and outer surfaces. As these organs mature they 

 gradually again metamorphose, but into a hardened body, and yet meanwhile, 

 or for a time, preserve one or two of the main characters of a leaf ; — the arrange- 

 ment of the bundles, &c., reminding one of the midrib and lateral veins of an 

 Angiosperm leaf, and the chlorophyll performing its function till near the time 

 of dehiscing. 



As soon as the ovules are fertilised, the lower portion of the macrosporophyll 

 gradually commences to thicken and close over them, thus forming a cryptic 

 character, as stated under article " The Origin of the Spur on the Cone Scale." 



After the closing period the sporophylls thicken until the full size of the 

 cone is reached. This process of thickening is marked by the bundle shown in 

 the various micro-leaf sections, commencing to be augmented and increasing in 



