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474 UK. A. AKBER ON THE LEAF-TIPS 



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leaf of Musa Basjoo, Sieb., with the apex intact, and two slightly older leaf- 

 tips of Mnsa CavendisJdi, Lamb. The structure of the apex seems essentially 

 identical iu both species. In Musa Ba,yoo, the main part of the limb is flat 

 and dorsiventral, but rolled in a counter-clockwise fashion in the bud. 

 There is a single row of normally orientated bundles, but the marginal 

 strands are highly peculiar ; they each consist of a mass of tracheids, many 

 of which are of unusu;il diameter, extending laterally outwards from the 

 bundle nearest to the leaf-edge (t.m. in fig. U a). The transition to the 

 more or less cylindrical apex is shown in fig. 14 n. 



In fig. 14 C the fusion of the two lateral vascular masses has produced an 

 arc of traeheids facing the midrib {t.a.) ; the ground-phin of the vascular 

 system at this stiige thus approaches that of a petiole rather than a lamin:i,and 

 T think we are justified iu regarding the cylindrical tip as being, just as in the 

 case of Smilax, the relic of an unexpanded petiohir apex. The superficial 

 cells secrete mucilage, and it may be that the survival of the solid tip is to be 

 associated with its value in the economy of the bud. It is interesting to 

 find that the Musacca), besides being the members of the Scitaminea) in 

 which the limb is normally characterised by the soliil apex, which uo have 

 just drscribcd, are also the Family in which the floral specialisation has 

 remained at a lower level than in the rest of the Cohort. I believe that there 

 is a connection between these two facts, and that the survival of the solid leaf- 

 apex — being a vestigial feature— is naturally associated with other primitive 



characters. 



It is known that the solid leaf-apex of Calla palustns serves as a hyda- 



thode *, but this fact docs not disprove the petiolar view of its morphology ; 



it may be that the vestigial petiole apex has been retained because it has 



assumed the secondary hydathodo function. It will be recalled that botl 

 Calla and Anthurhim, with their hermaphrodite flowers, are members of the 

 less specialised tribes among tiie Araceco — that is to say, they belong to that 

 part of the Family in which traces of the phyllodic origin of the leaf might 

 reasonably be looked for. But the fact that the solid leaf spaces are also to 

 bo found ill Viejcnhachia and Fhilodemlron shows that in the Araccre this 

 structural peculiarity is by no means confined io members of the more 

 generalised tribes. It is possibly, however, more than a mere coincidence 

 that, both in Smilax, the Musaceso, and certain Aroids, a pseudo-lamina with 

 a solid tip is associutod witli other characters wliich indicate that the plants 

 in question are rehntlvely primitive members of their respective 'cycles of 



affinity. 



There are considerable differences in the morpholot^y of the pseudo-lamina 

 in different families of Monocotyledons, and it would perliaps be rash to 

 generalise about the interpretation of the apex of such a blade iu the cases iu 



* Vollcens, G. (1883). 



