of a limiting velocity of 2-4 to 3 ft. per sec. after a drop of only 3 ft. or so from the 

 cone. Range for the seeds of the same tree may be considerable, according to 

 variations in length and width of wing ; average measurements suggest as normal : 

 Pinus excelsa, 3 ft. per sec. ; Picea Morinda, z-g ; Cedrus Libani, 2-7 ; P. austriaca, 

 2-3 ; the general approximation of different genera being very close. With such 

 a limiting velocity it is clear that, given air-currents deflected from the surface of the 

 ground with a vertical component of 2 miles an hour, the seeds would not fall at all, 

 but might be indefinitely drifted or whirled upwards. Such generalizations apply 

 to other winged seeds and fruits of Angiosperms, but no case gives more efficient 

 or more uniform results for the material and mechanism. It may be added that 

 Cedrus, with wing broadened distally in correlation with the broad cone-scale lamina, 

 presents no apparent advantage. Seeds without endosperm, being lighter, are less 

 efficient. The 2 seeds of one scale spin in opposite directions ; the edge nearer the 

 middle of the scale is ' anterior ' in spinning. 



Failure of the cone to ' open ' again may follow from (i) excessive and uniform 

 sclerosis in xerophytic types (P. muricata, P. clausa), or from lack of sclerosis 

 (P. Cembra) and insufficient differentiation. Similarly, the wing-mechanism of the 

 seed may fail as the seeds become too massive by thick sclerosed testa and bulky 

 endosperm (P. Pinea, P. edulis, P. Cembra'). 



The third case of the abscission of the cone as a whole follows normally in 

 response to xerophytic demands for the elimination of structures wasting water- 

 supply ; and spent cones are dropped (Pinus (sp.), Picea] though not in the deciduous 

 Larix. Many of the more massive cones are not abstricted, apparently owing to 

 difficulties in such cladoptosis (P. insignis] ; and this is emphasized in the case of the 

 non-opening P. clausa, &c. In P. sylveslris, grown under favourable conditions, 

 cones may remain on for several years, but some are shed at every dry spell through- 

 out the summer. Analogy of the case of the microstrobilus suggests that there is no 

 reason for regarding the persistence of the cone as a primitive feature, much less its 

 non-dehiscence, or the absence of spinning wings ; these last factors are common to 

 all the older races of the Abietineae without exception, as a part of their fundamental 

 equipment, probably dating far back to the common ancestors of this entire sub- 

 group. (Shaw, 1914.) 



The fourth case of the abscission of a structure even beyond the floral axis (as an 

 inflorescence-region) does not arise. Even in Taxus the abscission of the seed 

 leaves the basal part of the reduced parent-shoot. Hypotheses regarding the Pine- 

 cone itself as an inflorescence lead nowhere, and have no convincing foundation. 

 (Worsdell, 1900.) 



XI. Relation of Form-factors to Phylogeny and Classification. The 



preceding headings should suffice to indicate the normal trend of xeromorphic 

 specialization as affecting the general space-form of the tree and its lateral axes, 

 taken from the standpoint of vegetative shoot-systems (photosynthetic),and reproduc- 

 tive systems (flowers and cones). It is obvious that progression may take place in 

 any type, or in any groups of types, in any one of these directions, and in any one 

 respect, more or less independently of the others, though ' associated factors ' of 

 the same class may suggest ' family characters '. So varied are the manifesta- 

 tions in different degree for each factor, that it is not possible to arrange the 

 members of the whole group in any linear series, taking all the factors into 

 consideration together; though it may be done approximately for one factor at 

 a time. Even then only the morphological construction has been so far considered, 

 and a further multitude of factors similarly affect the details of the anatomical 

 organization of stem, timber, and foliage-needles, as also the details of the sexual 

 generation, the sexual organs, and the sexual cells. The balancing up of this 

 consensus of factors constitutes the method of approaching the discussion of the 

 phylogeny of the race, and the possible relationship of the different genera. The 

 degree of success attained in this direction depends on the exact valuation of the 

 different factors. This has been so far very vaguely done, and all suggestions as to 

 exact classification remain wholly provisional. Three main standpoints may be taken up, 

 as based on (i) tissue-anatomy, (2) on structural morphology, (3) on reproductive 



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