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ANATOMY, AND LIFE-HISTOBY OF THE CONIFERS. 



277 



whole bud is of a globose form ; and if a vertical section be made 

 of it, the axis will be seen to terminate in a dome-shaped process 

 from the sides of which emerge the perular leaves, each with a 

 "needle" in the axil. Strasburger describes these perulae as 

 traversed by a single mesial bundle, and this is probably true> 

 although in many cases I have found the structure to be wholly 



cellular. 



through 



Mohl 



shows the two to have a common cellular basis, so that it is not 

 possible to say where the one ends and the other begins. The 

 needle is longitudinally grooved in the centre of both upper and 

 lower surface, the furrow being deepest on the lower surface. 

 It is traversed by a double vascular bundle, and on microscopic 

 examination the structure is seen to consist of a bounding epi- 

 dermis with subjacent hypoderm, palisade-tissue traversed by 

 resin-canals, each surrounded by strengthening-cells and over- 

 lying a ground-tissue consisting of what Von 

 transfusion-tissue with large isolated stelliform sclerotic cells. 

 In the centre are two bundles each with its own bundle- 

 sheath. 



The pericycle consists of small, globular, closely-packed cells - 

 the xylem is on the underside (contrary to what happens in a 

 true leaf), its rays running obliquely upwards and outwards from 

 the base. This oblique position of the xylem is a fact of some 

 interest in connection with that interpretation of the nature oi 

 the seed-scale of Abietine® which postulates the presence of two 

 leaves arising from a contracted or undeveloped axis and having 

 a direction like that of the vascular bundle of Sciadopitys. 



"With regard to the two-fold nature of the bundle in Sciadopitys, 

 it may be pointed out that a similar two-fold or two-branched 

 bundle occurs in numerous species of Pinus, Picea, Abies, &c. ; 

 but in these cases there is but one bundle-sheath encircling the 

 two divergent masses of xylem and phloem, while in the seed- 

 scales of Abietineae no sheath at all is observable. The situation 

 of the xylem at the lower side of the needle and its divergence 



from the lower surface P \ / are in marked contrast to the 



X X 



position of the same elements in the leaves oi Pinus, in which the 



xylem is beneath the upper surface / 

 810118 converge from the base. P 



\ and the two divi- 





different opinions held with regard 



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