610 SUMMARY OF CURRENT RESEARCHES RELATING TO 



protoxylem is formed of spiral and annular vessels ; the metaxylem is of 

 wide tracheids, either scalariform or with several rows of pits. The 

 endodermis is of two or three layers, the innermost cells having thickened 

 radial and transverse walls. The lacunae of the middle cortex do nor 

 communicate with those of the middle cortex of the stem. The roots 

 have a firm outer cortex of thick-walled cells. 



Types of Embryo-development in Selaginella.* — H. Bruclimann 

 demonstrates that Selagindla Martensii, on the one hand, and S. Poulteri 

 and S. Kraussiana on the other, possess two different types of embryo- 

 development — a difference which is characterised by the original 

 position of the primary rhizophore. In S. Martensii the first rhizo- 

 phore arises between the foot and suspensor. In the other type it 

 arises above the suspensor and foot. Although systematists have 

 arranged the species in different groups according to their external 

 characters, it does not follow that these groups correspond with the 

 differences of structure shown in the embryo. The development of 

 the embryo in each of the two types referred to is described in detail, 

 and at the end of the paper a summarised comparison is appended. 



Bryophyta. 



(By A. Gepp.) 



Harpidium Section of Hypnum.j — J. A. Wheldon discusses the 

 classification of the difficult group of mosses, the Harpidia adunca of 

 Sanio. He gives several reasons for not accepting Renauld's view, that 

 Hypnum aduncum, H. Sendtneri, H. Wilson/, and H. lycopodioides 

 should all be regarded as sub-species of H. aduncum. Nor does he 

 accept Ingham's view that H. pseudoftuitans is a state of H. aduncum 

 {typicum). In the light of his own observations, he holds that the 

 varieties typicum, intermedium, and pseudoftuitans are not convertible 

 into one another by wetter or drier conditions. The problem is much 

 more complex. Hardly anything is known of the ecology and phy- 

 logeny of the mosses. Why do some mosses have straight leaves, and 

 others falcate ? The branching of the moss-stem is not determined 

 merely by such factors as light and shade, vertical or lateral illumination. 

 In attempting to trace the conversion of one species into another in this 

 critical group, the student must avoid being misled by badly developed 

 specimens. The author then gives an account of his own field observa- 

 tions on the following species or groups in the neighbourhood of 

 Liverpool during a period of fourteen years : — Hypnum aduncum Ren.. 

 H. Sendtneri Schimp., H. Wilsoni Schimp. The numerous forms of 

 H. aduncum are plentifully represented ; those of the group Kneiffii are- 

 found chiefly inland and less in pools near the coast, whereas the groups 

 pseudoftuitans and typicum occur near the coast only. As to H. Sendtneri, 

 regarded as an Alpine plant on the Continent, in this country it is con- 

 fined to the plains, and especially to the vicinity of the sea-coast. 



* Flora, xcix. (1908) pp. 12-51 ((figs.). 

 t Rev. Bryolog., xxxv. (1908) pp. 85-94. 



