214 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the Mesophytes, which also give rise to the Muscineas. The Amentales 

 show traces of their relationship to the Musciuese, and in some 

 respects resemble the Gjmnosperms, more especially the Gnetaceae. 

 The Cupuliferfe, although higher than the Casaarinea^, have diverged less 

 from the direct line than the Myricineae ; the other families — Salicineee, 

 Piperineas, Chloranthinese, and Juglandaceag — start at different levels 

 from the branch which terminates in the Myricaceae. S. G. 



CRYPTOGAMS. 



Pteridopliyta. 



Contribution to our Knowledge of the Vascular System of the 

 Genus Equisetum. — Kate Barratt (Ann. of Bot., 1920, 34, 201-35, 

 2 pis. and figs.). An investigation of the anatomy of the sporeling 

 and the development of the vascular system. 1. The sporeling of 

 E. arvense is protostelic at its base, siphonostelic where the vascular 

 supply of the secondary axis is attached, and protostelic again for a short 

 distance below where the first whorl of leaves is attached. 2. The basal 

 regions of the succeeding axes of the young plant possess a compact 

 closed siphonostele composed of short reticulate tracheids. There is 

 thus formed a sympodial vascular tube in which five or more axes may 

 be concerned. 3. The secondary axis arises endogenously from the 

 primary axis below the level of the first leaf -whorl. 4. The vascular 

 structure of an anomalous tuber is described, in which carinal canals are 

 formed in connexion with the protoxylem, and these in the middle 

 region of the tuber are enveloped by separate endodermis. 5. A young 

 sporeling of E. limosum is described showing a forked primary axis. 

 The arrangement of the vascular system indicates that it has almost 

 certainly arisen by a dichotomy. 6. Secondary thickening of the nodes 

 of B. arvense and E. maximum was studied in the light of the develop- 

 ment of the nodal tracheids ; and the conclusion was arrived at that 

 the apparent increase in elements, which has been attributed to secondary 

 thickening, is due to the enlargement and displacement of developing 

 tracheids. 7. The vascular structure of the cones of E. arvense, E. 

 maximum, E. paliistre, E. limosum, and E. sylvaticum is described. 

 The endogenous protoxylem strands are shown to form complete and 

 continuous systems, uninterrupted by nodal tracheids, as is invariably 

 the case in vegetative shoots. The metaxylem develops later, and varies 

 in amount and distribution in the different species. E. arvense shows 

 the greatest amount, and E. limosum and E. sylvaticum the least. It is 

 concluded that the gaps in the metaxylem siphonostele cannot be 

 described as leaf-gaps, bearing no relation to the sporangiophore traces, 

 but may be related to the mechanical efficiency of the cone. It is also 

 concluded that the vascular structure of the cone indicates that the 

 sporangiophores are not the morphological equivalent of leaves, but are 

 organs sui generis, and the axis of the cone is undifferentiated into node 

 and internodes. 8. The general vascular system of the plant is dis- 

 cussed, and it is concluded that the general plan of development proceeds 



