SCIENCE- G OS SIP. 



*59 



extinct form of Uqmsetiim, of which fig. 1 is a 

 sketch. It is interesting, from the fact that at the 

 " node " (see fig. 1, a) one can detect the method of 

 bundle-splitting and reunion as evidenced by the 

 lines of ribs, and in a few places remains of leaf- 



Fig. 1. Fossil Stem of Extinct Equisbtum. 



a. Node. b. Portion of node magnified to show method of 

 bundle-fusion and reunion. At x leaf-scars are seen. 



scars. I have also found near the same spot a few 

 specimens of parts of fossil Filicineae, showing the 

 characteristic scars at points where the fronds 

 sprang from the main axis. — H. A. H. 



The Vascular System in Mosses. — The stem 

 of a moss plant, arising as it does from a simple 

 structure, the protonema, is a simplified form of 

 axis from which spring numerous spirally arranged 

 leaves ; sometimes the axis is bilateral, and in 

 many cases branches are given off. On transverse 

 section such a stem shows, when examined micro- 

 scopically, epidermis, a fundamental ground tissue 

 or cortex, and a central portion, the outer part of 

 which consists of sclerised elements, the inner of 



(See fig. 2.) The existence of spirally thickened 

 tracheicles is interesting, from the fact that we have 

 here one of the first instances of vascular differen- 

 tiation in plants, working from below upwards. In 

 the lower orders, Thallophyta, there are cases 

 where external similarity to a stem may occur, as 

 in Fucaceae, but there is no true internal vascular 

 differentiation ; the function of upward conduction, 

 if there be any, being shared by all the cells of 

 the thalloid structure. This may partly be the 

 case in Musci, but the central stem and leaf tissue 

 seems most suited to upward conduction. The 

 laminae of the leaves are only one cell thick, and 

 evaporation from the free surface thus goes on 

 without the intervention of stomata. It seems 

 probable that there is a fairly strong transpiration 

 current, and this is likely to be much reinforced 

 by direct evaporation from the outer-lying cells of 

 the cortex of the younger branches. 



Some Kecent Kesults in Photo-micro- 

 graphy. — -Mr. Dennis, in the " Journal of Applied 

 Microscopy," pp. 1-5, August 1901, describes a 

 method whereby he has recently obtained high- 

 power ( x 1,500 diams) photo-micrographs of various 

 structures. There are some excellent reproductions 

 from these of certain stages in karyokinesis, taken 

 from the rootlet of Allium, and dividing pollen- 

 grains of Lilium ca-rulicluvi. The method employed 

 has the advantage of a great degree of rigidity, a 

 factor which is of first importance. 



Effect of Light upon Chlorophyll-plate 

 in Mougeottia. — The intrinsic and other move- 

 ments observed in the chloroplasts of leaf-cells 



Pig. 2. Optical Section of Moss-leaf. 



a. Spiral tracheide in centre of leaf. b. Thick-walled sclerenchymatous 

 elements forming a strengthening layer, c. Assimilatory cells of leaf. 



elongated vascular " tracheicles," which generally 

 show some spiral thickening. The same sort of 

 central tissue occurs in the leaves, where it is 

 called a midrib, and is several cells in thickness. 



p a n py 



Fig. 3. Single Cell from Filament of Mougeottia. 



a. Cell-wall. p. Peripheral protoplasm, n. Nucleus. 

 I: Flat chlorophyll-plate, py. Pyrenoids. 



under the influence of light of different degrees 

 of intensity are, as is well known, of great im- 

 portance in determining the opti- 

 mum amount of assimilation for 

 any given green organ. An inte- 

 resting instance occurs in one of 

 the Conjugatae, Mougeottia, a fila- 

 mentous alga somewhat resembling 

 Sphrogyra, but differing from this 

 latter in having a flat plate-like, and 

 not a spirally wound, chlorophyll 

 body. On exposure to light of 

 moderate intensity, such as diffuse 

 daylight, this plate is seen to take 

 up a position calculated to enable 

 it to receive light at vertical inci- 

 dence. In direct sunlight the plate 

 presents its edge to the incident 

 rays, and in light of varying degrees 

 of intensity all intermediate posi- 

 tions may be taken up. In the 

 accompanying fig. 3 the plate is in 

 such a position as to receive rays of light perpen- 

 dicular to the plane of the paper. 



Note. — Several important papers upon Physio- 

 logical Botany await space for insertion. 



