490 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of thickenings in the wall ; the second including the development of the 

 thickening-layers. In their youngest stages the mothor-cells of the 

 peristome do not differ in any way from ordinary meristematic cells. 

 The nucleus acquires after a time a crescent shape. During the first 

 period of development the movements and other changes in the cyto- 

 plasm of these cells are not directly dependent on the influence of the 

 nucleus. The nucleus of these cells at first increases in size, hut again 

 diminishes after the commencement of the thickenings in the wall. 

 The number of nucleoles in the nucleus increases and again diminishes 

 in proportion to its increase and decrease in size. The formation of 

 the thickening-layers of the membrane is directly dependent on the 

 activity of the nucleus. The thickening-layers are composed, at all 

 events in their early stages, of cellulose and pectinaceous substances. 



Branching" in the Hepaticae.* — Mr. A. W. Evans records a new type 

 of branching in the leafy Hepaticae. According to Leitgeb, the terminal 

 branching always occurs in this group in the ventral half of one of the 

 lateral segments cut off from the apical cell. Bui in Mastigobryum 

 integrifolium (Hawaian Islands) it takes place in both lateral and 

 ventral segments. 



Acromastigum, a New Genus of Hepaticae. f — Mr. A. W. Evans 

 separates from Mastigobryum a liverwort from the Hawaian Islands, 

 as the type of a new genus Acromastigum, with the following dia- 

 gnosis : — Plants medium-sized, yellowish-green, becoming brownish 

 with age; stems stiff and wiry, mostly ascending or erect, sparingly 

 branched ; vegetative branches of three kinds — terminal branches from the 

 lateral segments, " flagella " from the postical segments, intercalary 

 branches axillary to the under-leaves ; leaves distant or subimbricated ; 

 leaf-cells with thickened walls ; sexual branches intercalary ; 9 branch 

 very short ; perianth long and slender ; unfertilised archegones borne at 

 the base of the calyptra ; $ spike oblong ; paraphyses wanting. Sporo- 

 phyte not seen. 



Algae. 



Tension and Passive Growth in Seaweeds.} — Herr E. Kiister has 

 examined the condition of tension in the " tissues " of a number of 

 marine algae belonging to the Cyanophyceas (Itivularia polyotis), Chloro- 

 phyceae (Codium bursa), Florideae, and Fucaceae (especially in the swim- 

 bladders). He lays it down as a general law that a pressure-tension is 

 the condition in the cortex, a traction-tension iu the pith. Minor 

 differences exist from the fact that in the Florideae we have a compact 

 complex of much-branched hyphae-like filaments ; while in the Phaao- 

 phyc-ese we have intercalary cell-divisions, with a strong tendency to 

 proliferation. With the unicellular Codium the conditions of growth 

 are quite different, but the general law of tension ajipears to be the same 

 in all cases. 



Index of Desmids.§ — This most useful book of reference, by Prof. 

 C. F. 0. Nordstedt, commences with a very complete alphabetical biblio- 



* Bot. Gazette, xxix. (1900) p. 140. 



t Bull. Torrey Bot. Club, xxvii. (1900) pp. 97-104 (1 pi. and 2 figs.). 

 j S.B. k. Preuss. Akad. Wiss. Berlin, 1899, pp. 819-50 (1 pi.). 

 § ' Index Desmidiacearum citationibus locupletissimus atque Bibliographia,' 

 Berlin [1900], 310 pp. 



