29G 



0)i the Comparative Anatomy of Flowers. [Dec. 22, 



II. " A Contribution to the Study of the Comparative Anatomy 

 of Flowers." By Rev. G. HENSLOW, M.A., F.L.S. Com- 

 municated by Dr. B. W. Richardson, F.R.S. Received 

 December 2, 1887. 



(Abstract.) 



The author first drew attention to the importance of the class of 

 observations illustrated in this paper ; for by referring all the floral 

 organs back to their vascular cords, or " axial traces," their real 

 origins could be discovered, whenever their developmental history 

 was incapable of showing them. 



Taking the cords as " floral units," he showed how they can give 

 rise to axes as well as all kinds of floral appendages. The two ele- 

 ments of which a cord is composed are tracheae or spiral vessels and 

 sieve-tubes, &c. or soft bast. The significance of the relative posi- 

 tions of these two elements was pointed out, and M. Ph. van 

 Tieghem's distinction between axial and foliar characters of cords, 

 I.e., in having the tracheae on the side of the medulla in the former, 

 and on the outside in the latter, was criticised as being by no means 

 constant, especially as regards the floral cords ; inasmuch as a more 

 general rule is for the tracheae of the latter to be exactly central or 

 scattered irregularly in a groundwork of phloem. 



After describing the arrangements in peduncles and pedicels in 

 which endogens often have their cords as regularly placed as in 

 exogens, the author explained the different ways by which pedicels 

 of umbells are formed in each class respectively, and how they are 

 supplied with cords from the common peduncle. 



He next pointed out the phyliotactical origin of the number of 

 parts in floral whorls, and how the various arrangements of their 

 members become altered in consequence of the union of their cords 

 below, so that the proper angular divergences are not maintained, 

 and parts often become superposed which would otherwise alternate 

 in position. 



The union, separation, reunion and fusion of cords, as well as the 

 way in which they may shift their positions, were discussed, and the 

 effects produced by such processes were explained. 



The results of the multiplication of parts brought about by 

 " chorisis " of a cord were illustrated ; whereby a simple cord of a 

 pedicel could give rise to any number of floral parts, such as the 

 members of different whorls, as in the case of Campanula medium, in 

 which a simple axial cord supplied a sepaline, a dorsal carpel! ary, a 

 staminal and half a petaline cord : or when a repetition of the same 

 kind occurs, as in double flowers. 



