lowest ovules being buried lomm. in the rounded base of the mass, now 40-50 

 long, and the majority are 5-8 mm. beneath the surface. 

 Special points to note as distinct factors are : 



(1) The precocity of the mucro, its vague function and early cessation of 



growth. 



(2) The primary sealing of the system by intercalary growth in the region 



below the mucro (cone-scale). 



(3) The secondary sealing by apophysial facets in the second year. 



(.j) The parallel elongation of the cone-scales, and its relation to the extension 

 of the seed-wings. 



(5) The cones are sterilized at both ends, with an output restricted to 40-50 



seeds in the region of optimum protection. 



The entire cone remains soft and succulent until fertilization has been effected 

 (June 25). Similar observations may be checked on the more elongated cones of 

 P. Strains and P. excelsa, in which sterilization of the basal region is less pro- 

 nounced ; the apophyses do not attain a peltate expansion, but are sealed by similar 

 papillose growths. 



It is now seen that Pinus (more particularly 2 -needled forms), as the most 

 highly specialized type, combines a number of secondary features of mechanism 

 devoted to the same end, as : 



(1) extreme limiting reduction of the original bract-scale (megasporophyll), 



(2) inversion of the ovules, 



(3) fusion of these to the cone-scale along one side, 



(4) great extension of the sealing crest (or ' cone-scale '), 



(5) the latter precociously functional in the pollination stage, 



(6) with primary growth (umbo), 



(7) secondary apophysis facet, 



(8) sealed in close contact at the surface, 



(9) the scales become wholly sclerosed and contain little vascular tissue. 



The controlling factors are the necessity of a sealing mechanism, and the manner 

 in which this is met by new growths in a basal intercalated zone, the position of 

 which may be indicated by the original carpellary leaves even in their last phases 

 of vestigial development. 



IX. Cone-factors : The archaic strobilus-habit is traced more clearly in the 

 case of the axes bearing microsporophylls because these are of relatively ephemeral 

 nature ; they only require bud-protection during the maturation of the pollen-grains, 

 and this is effected by condensation of the structure and the overlap of vestigial 

 imbricating laminae ('connective flaps'). After the discharge of the pollen they 

 merely shrivel, dry up, and are cast off. 



On the other hand the strobili of megasporophylls which become the ' cones ', 

 require to be still more efficiently protected during the stages of prothallial develop- 

 ment, and to be supplied with large stores of food-material, as also water, from 

 the main axis, over the period of fertilization, the development of the embryo, and 

 the storage of reserves in the seed-stage. Where xerophytic conditions obtain the 

 cone-structures will feel the drain of the environment possibly more than any other 

 part of the plant ; the new functions are in themselves associated with problems of 

 economy in the water-supply to the aquatic sexual phases (seed-habit) ; and as the 

 cones and their included parasitic generations living at the expense of the other 

 tissues can only obtain water in competition with the transpiring foliage, extreme 

 xerophytic specialization thus affords the clue to the organization of the ' adult ' 

 cone, as expressed more particularly in : 



(i) Shape, (2) Size, (3) Scale-protection, (4) Succulence, (5) Woody (sclerosed) 

 texture, and (6) as subsidiary details tending in the same direction, inversion, resin- 

 exudation, cuticle- and cork-formations. To these may be added number of scales, 

 ovules, and seed-output ; but these last points, though significant in the individual 

 cone-axis and the branch bearing it, are less significant in that such problems involve 

 the further total output of cones and seeds in the entire tree. 



(i) Shape: The original strobiloid form as a cylindrical elongated mega- 

 strobilus is most clearly expressed in forms of Abies (A. nobilis, clothed with adpressed 



17 



