560 SUMMARY OF CURRENT RESEARCHES RELATING TO 



table kingdom (previous to the publication of de Vries's " mutation; 

 theory "). It is impossible to refer all the phenomena with which we 

 are acquainted under this head to similar causes. In contrast to the 

 phenomena of domestication or artificial selection, the author considers 

 that in nature, natural selection is only of indirect importance in the 

 production of new forms. Characters derived from organisation are 

 modified by the fixing of those connected with adaptation, by crossing 

 and by heterogenesis. 



B. CRYPTOGAMIA. 

 Cryptoganiia Vascularia. 



Anatomy of Loxsoma.* — Using Van Tieghem's term solenostelic 

 in preference to the one in more common use, gamostelic, D. T. Gwynne- 

 Vaughan defines a solenostelic stem as one in which the vascular tissue 

 is arranged in a single hollow cylinder, with phloem and phloeoterma on 

 either side, the complete continuity of which is interrupted only by 

 the departure of the leaf-traces, the gaps thus produced being closed 

 up in the internode above before the departure of the next leaf-trace. 

 In the case of ferns, where this structure occurs more often than in 

 other classes of vascular plants, the solenostelic arrangement of the 

 vascular tissue is probably more primitive than the polystelic. Ac- 

 cording to Jeffrey's terminology, f the anatomy of ferns may be 

 regarded as a special type of " amphiphloic phyllosiphony." 



In Loxsoma, which belongs to the solenostelic type, the stem is 

 characterised by the occurrence of scattered islets of parenchyme among 

 the sclerotic general ground-tissue. The protoxylem proper to the stem 

 consists of narrow scalariform tracheids evenly distributed around the 

 external periphery of the xylem-ring. The root presents no special 

 peculiarity of structure. In a transverse section of the petiole the 

 vascular strand has a horse-shoe form. The protoxylem elements of the 

 petiole, which are spiral and annular, are collected into definite endarch 

 groups. 



As regards its affinities, Loxsoma is, on the side of its anatomy, 

 more nearly related to Dennstaedtia (Diclcsonia) and to the solenostelic 

 Polypodiaceae than to any other family of ferns. 



K. Giesenhagen % points out an inaccuracy committed by Mr. Gwynne- 

 Yaughan in quoting his description of the vascular system of the 

 Hynienophyllaceae. 



Muscineae. 



Conducting 1 Tissue-System of Bryophyta.§ — A. G. Tansley and 

 Miss Edith Chick describe the structure, and discuss the origin, of the 

 conducting tissue of Bryophyta, which must be of a totally different 

 origin from that of Pteridophyta, since it is confined mainly to the 

 gametophyte generation. 



In the Hepaticae, as a rule, there is no differentiated water-con- 

 ducting tissue ; but in three genera — Pallavicinia, Symphyogyna, and 

 Hymenophyton — most of the species of which are tropical, a portion of 



* Ann. of Bot., xv. (1901) pp. 71-99 (1 pi.). t Cf. this Journal, 1900, p. 686. 

 X Tom. cit., pp. 433-4. § Tom. cit, pp. 1-38 (2 pie.). 



