TRAKSACTIONS Of" SECTION K. 835 



numerous in proportion to Ferns ; there is no reason why they should not be, 

 if both are equally ancient. 



The enormous antiquity of highly organised Gymnospermous wood, e.g., 

 Callixylon Trifi/ievi in the Upper Devonian, Palce<ypitys Miileri in the Middle 

 Old Ked Sandstone, suggests, if it does not prove, that Hpermophyta go as far 

 back in geological history as any land plants of which the structure is known. 

 Hugh Miller, three-quarters of a century ago, rightly insisted that the Gymnogens 

 and Acrogens, as he called them, formed two parallel lines, running back into 

 the unlinown past. We cannot but believe that the two lines converged some- 

 where, but it may well have been at a point so remote that the common source 

 antedates the origin of the Pteridophyta as hitherto understand. 



2. On some New Types of Statocyte occurring in Vascular Plants. 



By Miss T. L. Pkankerd. 



Further work has necessitated a slight modification of the definition of a 

 statocyte given to the Section in 1915, and I now propose to define the term as 

 a cell containing a body or bodies more or less free to move under the influence 

 of gravity. The varied types may be characterised as follow : — 



(1) The statoliths, or moveable bodies, are starch grains [amylostatoliths] , 

 simple or compound, larger than, smaller than, or the same size as the embedded 

 grains of other tissues. 



(2) The statoliths are starch-containing chloroplasts (cJilorostatoliths). 



(3) The statolith is a crystal of calcium oxalate usually occurring singly in the 

 statocyte. 



(4) Similar to (1), but the nucleus is differentiated in size and staining 

 capacity from the nuclei of adjacent cells. 



(5) Similar to (1), but the nucleus occupies a definite position in the cell, and 

 though apparently free from the statoliths, moves with them. 



(6) The nucleus is more or less united to starch grains, or starch-containing 

 chloroplasts to form a gravitational unit [nucleostatoiith). 



(7) The statocyte is elongated in a vertical plane and contains a thick strand 

 of protoplasm attached at each end. The strand contains embedded starch 

 grains and a central nucleus, and is capable of swinging to the lower side of the 

 statocyte should the latter be displaced. 



Of the above (3), (4), and (7) are probably rare. The rate of movement varies 

 very considerably in different plants ; by far the highest yeE discovered is that 

 of the crystal statolith in the wheat plant, which is 600 microns per hour, i.e., 

 at least three times that of any other known statolith. 



Quite independently of any function which may be attributed to statocytes, 

 they are definite histological imits, generally aggregated together into a tissue 

 (State.nchyma) — a no less definite feature in plant anatomy. 



3. The Flora of the District of the London Clay. 

 By Horace W. Monckton, Treas.L.S., F.G.S.'' 



The present communication deals with the Thames Basin only. The flora 

 of the London Clay differs greatly from that on the other geological formations 

 of the district, more especially from the flora on the chalk or on the Bagshot 

 Beds. 



The sedges are taken as an illustration. About twenty-eight species, and 

 the hybrid Carex axillaris, grow on London Clay. Eleocharis palustris, C'arex 

 vulpina, C. panicea, C. ftacca, C. hirta, and species of the flava and riparia 

 groups are abundant. C. pulicaris, C. stellulata, C. elongata, C. pillescens, 

 C. Pseudo-Cyperus, C. sylvatica, and C. vesicaria may also be mentioned. 



In addition to the twenty-eight species referred to above, there are some 

 twelve others recorded from the London Clay area. These include Bynchospora, 



^ See ' The Flora of the Bagshot District,' in Journ. of Botany, Vol. 57, 

 September, 1919. 



