C. Lawsom'ana, laterals of Larix}. The free ends of laterals carried well beyond 

 their fellows may erect (Sequoia gigantea, Thuya gigantea, Cryptomeria), but this in 

 Larix would be regarded as a freak, as a phase of the mechanism which will 

 reorientate a new leader if the main axis is damaged. Dwarf-forms lacking erected 

 leaders give prostrate plants, as Meadow Spruce, dwarf Juniper, and dwarf Pinus 

 montana (P. Mughus], and such forms may be maintained in cultivation, as by 

 grafting. 



((3) Beyond mere orientation of normally produced branch-systems, a conspicuous 

 example of which is noted in Cedrus, with the spur-shoots all orientated vertically to 

 the upper surface of the laterals, the effect may extend to the initiation of lateral 

 ramifications of higher degree, as in Araucan'a, in which laterals of second and third 

 degree are formed in flanking orthostichies only of the main shoot to produce the 

 special bilateral frond-effect (A. excelsa). Although this can be effected fairly satis- 

 factorily in terms of spiral construction, the result will be much more precise when 

 based on a preceding condition of symmetrical leaf-arrangement; and thus in 

 Cupressineae with decussate phyllotaxis giving bilateral symmetry to begin with, the 

 arrangement is extended to the production of laterals only from the axils of 2 series 

 of leaves out of the 4. This sequence may be maintained for 2-3-4 degrees of 

 ramification in the same plane of bilaterality, resulting in the familiar phyllomorphs 

 of this section, in distinct generic forms (Thuya, Libocedrus}. 



(y) A third phase of dorsiventrality is seen in the general twisting of leaf-petioles 

 to re-orientate the foliage-units themselves with reference to incident light. Spiral 

 systems thus present varying degrees of distortion as the members turn to the upper 

 surface, or form two flanking series culminating in more precise pectination in lateral 

 series (Taxus, Taxodium, Sequoia sempervirens, Tsuga, Abies pec tinata) ; and in many 

 cases the effect is confined to more horizontally placed laterals, while vertical shoots 

 retain the original spiral arrangement (Taxus, Sequoia sempervirens, Podocarpus 

 japonica), as a condition which has been loosely described as giving a dimorphic 

 shoot-system. 



(8) A further effect may be noticed in the associated orientation of the floral 

 shoots on dorsiventral branches, though the meaning of such response is not clear : 

 the effect is geotropically regulated. Thus the staminate flowers erect on the upper 

 surface of dorsiventral laterals in Cedrus and Araucaria, but turn downwards in Larix, 

 Abies, Pseudotsuga, and Taxus. On the other hand the carpellary flowers are erected 

 in Cedrus, Araucaria, Larix, and Abies, but are turned to the lower surface in Taxus. 

 In Biota they are horizontally projected, as also curiously in Cryptomeria, and more 

 or less inverted in Juniperus sphaerica. 



While dorsiventrality in the leaf-lamina is structural, following from the mechanism 

 of elaboration of a lateral leaf-primordium, however much it may be outwardly lost in 

 fairly isodiametric needle-leaves (Cedrus, Larix, 5-needlecl Pines), the dorsiventrality 

 of the branch-system is always secondary, and is superposed on a centric internal 

 organization, apparently in response to insolation, though the mechanism may be 

 largely controlled by geotropism. It is clear that different phases of dorsiventrality 

 may be attained independently in different types, to varying extent, and in unequal 

 degrees, as specific or generic constants ; e. g. Pinus exhibits slight dorsiventrality 

 only in primary lateral leaders ; Araucaria imbricata and A. excelsa to a much greater 

 extent in secondary and tertiary laterals as well ; Cupressus Lawsom'ana and C. Noot- 

 katensis illustrate the extreme condition of phyllomorph construction ; on the other 

 hand, Taxus only shows dorsiventrality in the pectination of the foliage-leaves and the 

 position of the flower shoots. Types with no specialization of dorsiventrality are less 

 frequent. It is practically wanting in Cryptomeria, little in Ginkgo, as also in 

 irimeiws, Juniperus communis. Loss of effective regulation may also affect one form 

 of dorsiventrality without necessarily involving another. The fastigiate habit is 

 apparently normal for Biota, giving radially orientated laterals with phyllomorphs, as 

 in fastigiate Cupressus Lawsom'ana (cultivated vars.) ; in Taxus the fastigiate variant 

 also omits the pectination of the foliage-leaves, but is so rare as to be regarded as an 

 occasional ' sport '. 



IV. Strobilus Factors : A generalized shoot-construction producing sporo- 

 phylls with wind-dispersed spores, compacted to a bud-formation for mutual protection 



7 



