402 SUMMARY OF CURKENT RESEARCHES RELATING TO 



of certain species of Equisetum, a condition most marked in ^. maximum, 

 is regarded as a derivative character, due chiefly to the reduction of the 

 radial extent of the metaxylem. (5) Parenchymatous meshes of the 

 cone probably first arose, in the phylogeny, at points vertically above 

 the departure of the traces of sporangiopliores, and were not true gaps 

 (in Jeffrey's sense) ; and in cases where meshes arise very close above 

 the departure of the trace, this approximation is probably due to reduc- 

 tion of xylem during the phylogeny. The primitive system was 

 probably siphonostelic. (6) In the anatomy of E. sylraticum the 

 following points support the view that the insertion of the annulus 

 marks the position of a vestigial node : {a) the numerous anastomoses 

 of the axial strands at this level ; (b) indications of anastomosis of the 

 protoxylem at the same level ; (c) the presence in the axis opposite the 

 annulus of cone B of an abortive trace that never becomes free ; (d) 

 the presence in this same cone at the level of insertion of the annulus 

 of tracheides somewhat resembling those of the nodal xylem of the 

 vegetative axis ; (e) the occurrence, according to Milde, of branches 

 below the annulus. (7) In one of the cones of E. dehile four small 

 groups of vascular cells were observed in the parenchyma of the 

 annulus ; though unconnected with cells of the axial bundle, they 

 possibly may represent vestiges of the traces of the annular node. In 

 this species, however, and still more in E. variegatum, there are but 

 few indications of the former presence of a node at the insertion of the 

 annulus. (8) In some specimens of E. deh'le the ring of nodal (or 

 supranodal) xylem is not complete at the level of the uppermost whorl 

 of leaves. A. G. 



G-ametopliytes of Equisetum laevigatum. — Elda R. Walker 

 {Bot. Gaz., 1921, 71, 378-91, 2 plates and figs.). Prothallia of 

 Equisetum have rarely been found until recent years, but in August, 

 1916, large numbers were detected by R. A. Xesbit in Nebraska, 

 associated with Riccia on the mud belt of streams and rivers. The 

 investigation of numerous wild specimens gave the following results : — 

 The gametophytes are all of one kind. They consist of a flat circular 

 disc 1-10 mm. in diameter, bearing numerous upright green branches 

 on their upper surface, and surrounded by a band of meristem, which 

 continues the growth of the thallus and produces archegonia and 

 antheridia. They are typically monoecious, bearing some archegonia 

 and many antheridia, which are without order and often within a few 

 cells of each other and of sporophytes, and which may continue to 

 develop until one or more sporophytes have attained considerable size. 

 Antheridia all develop, as is characteristic of eusporangiate ferns, 

 whether in a massive tissue or on a slender br.snch. Archegonia de- 

 velop in manner characteristic of the group. Sporophyte development is 

 as described by authors. The leaves of the first shoot are three or four, 

 of the second shoot four or five. Gametophytes grow to maturity under 

 simple methods of culture. The germination of spores and raising of 

 young gametophytes under culture is quite easy ; but the spores must 

 be young and quite fresh. A. G. 



Eusporangiate Ferns and the Stelar Theory. — D. H. Campbell 

 {American Journal of Botany, 1921, 8, ;!0o-14:, figs.). A summary 



