LIXXEAK SOCIETY OF LONDON. 47 



I do not know if Tyndall's experiments have been followed up 

 by any botanist, but if not, I think this will form an interesting 

 subject for further investigation, 



April 2nd, 1903. 



Dr. D. T. Gavtnxe-Vaughan gave a lantern- demonstration of 

 his paper, " On the Comparative Anatomy of the Cyatbeaceae and 

 other Ferns." He stated that the vascular system at the very 

 base of tlie stem of a young plant of Ahojihila exceha, E. Br., is 

 found to be protostelie, and as it advances towards the more com- 

 plicated structure of the mature stem it passes through a series 

 of transitional stages which in certain other Ferns are retained as 

 the permanent structure of the full-grown plant. 



The first departure in the young plant from the protostelie type 

 of structure is due to the appearance of a core of phloem within 

 the substance of the xylem of the protostele. This gives rise to 

 a type of vascular structure which maybe found in DavaUla repens, 

 Desv., as the permanent structure of the mature stem. Then, in 

 the young plant, the endodermis and ground-tissue lying on the 

 adaxial side of the departing leaf -traces are prolonged downwards 

 into the internal core of phloem. These decurrent strands of 

 ground-tissue at first end blind!}- in the internal core of phloem 

 before reaching the node below, giving rise, in this manner, to a 

 type of stele which is also to be found in the mature stem of 

 DavaUia pinnata, Cav. T\'hen the decurrent ground-tissue be- 

 comes continuous from one node of the young plant to the other, 

 a solenostelic structure is reached entirely similar to that found 

 in the mature stems of a large number of different Ferns. 



It is suggested that this series of vascular types illustrates the 

 actual manner in which the transition from protostely to dictyo- 

 stely took place in the Cyatheacese and Polypodiacese. That is to 

 say, the ancestral protostele of these two orders never contained 

 a "definite pith, and its conversion into a solenostele was initiated 

 by the replacement of some of its xylem elements by phloem, 

 later on by endodermis and ground-tissue. This suggestion is not 

 in any way afl^ected by the question 'as to the cortical or stelar 

 nature of the internal ground-tissue. 



The xylem in the steles of Fern-stems seems to be differentiated 

 in two different ways. Either the protoxylem elements are moi'e 

 or less evenly distributed all round the periphery of the xylem 

 mass, or else they are localized in definite endarch or mesai'ch 

 strands. In the latter case the protoxylem strands of the stem 

 are ah^ays related directly or indirectly with those in the leaf- 

 trace. 



In the more primitive Pteridophyta in which the influence of 

 the leaf-trace upon the stem-stele is practically negligible, the 

 protoxylem is nearly always exarch, and it would seem that 

 endarchy originated in the leaf-trace and that, in general, it 

 appeared in the stem only when the influence of the leaf-trace 

 had begun to dominate the structure of the latter. 



