i9°9l 



THOMSON— SAXEGOTHAEA AND MICROCACHRYS 353 



Coulter and Chamberlain, after reviewing the different theories 

 of the fertile scale in their textbook on the gymnosperms, make the 

 following statement (p. 77): "Upon sifting the testimony certain 

 things seem to be fairly clear, and one is that the scale and its ovules 

 in Abieteae represent a highly modified axillary shoot, corresponding 

 to the characteristic spur shoot of the group." From anatomical and 

 teratological evidence this conclusion seems inevitable, and since the 

 Abieteae, Taxodieae, and Cupresseae present such a series of natural 

 affinities the statement must apply to all. If, then, the fertile scale 

 in this group is of the brachyblast type, representing the adaxially fused 

 first and only two leaves of an abortive axis, the first inversion is 

 explained, and the ovules in this group are borne on the morphologi- 

 cally under surface. The second inversion is analagous to the single 

 one in Saxegothaea and of the nature of a sporangial supply. There 

 are, then, two great groups of the conifers from the standpoint of 

 this study, the simple- and the complex-scale series. Both forms 

 have the ovules on the physiologically upper surface, a position ren- 

 dered almost imperative by the necessities of the seed habit. This 

 Position, however, has been attained in two very different, but pos- 

 sibly equally difficult, ways in the aplo- and diplosporophyllous 

 forms of the Coni ferae. ' 



Toronto University 



EXPLANATION OF PLATES XXII-XXV 



PLA TEXXII 



Fig. i.— Fruiting twig of Saxegothaea conspicua. Slightly enlarge . 

 Figs. 2, 3.— Micro- and megasporangiate cones. X4- 



Fig. 



plate XXI 11 



k 



the 



«g. 4.-Megasporangiate cone with the axis more eiu.. & — . . 



Fig. S--Microcachrys tetragona; micro- and megasporangiate 

 f °nner in mature condition. X4- 



Fig. 6.— Older megasporangiate cone. , ^_-» n f the 



. R* 7-9-Resperti vely radial, transverse, and tangent.al sect.ons of 



mi crosporangiate cone of Saxegothaea. attached- fig- 



ft**. 10, n.-Megasporophylls of Saxegothaea, with ovules attached, fig 



" show 'ng ovular supply coming off the main vascular bundle. 



PLATE XMV Caxesothaea, young 



Fig. 12.— Transverse section of the megasporophj 11 oi saxcg 

 condition, just proximal to the insertion of the ovule. 



