12 2 



HARDWICKE'S SCIENCE-GOSSIP. 



have been proved to grow in this county, one of 

 which had been found only once before in Great 

 Britain. And further, there are now, within the 

 writer's view, sundry recent local gatherings in glass 

 jars, which contain types of the only three genera 

 that have been found on the mainland of Great 

 Britain, all of which were gathered within three miles 

 of Luton. The fourth genus of British Characece has 

 been found only in the Isle of Wight. This is suffi- 

 cient to suggest that there is much room for original 

 work, in this section of botanical research. 



Some readers may also ask for hints as to the 

 modus operandi. The apparatus is simple enough : a 

 stout stick with an iron hook at the end is usually 

 sufficient. Sometimes one may cut a long hazel rod, 

 and fasten a few short lengths of dog-rose stem on the 

 end : the stout, recurved prickles of which will inva- 

 riably bring up specimens of any plants with which 

 they may come in contact. When secured and taken 

 home, it is necessary with the more delicate forms to 

 float them on the mounting paper under water : with 

 a little practice this may be done in a few minutes, so 

 that the paper and specimen may be withdrawn from 

 the water without injury to the former. Most of the 

 moisture should be then absorbed with drying paper, 

 before putting in press. The stouter forms may be 

 dried in the usual way. Although somewhat difficult 

 of manipulation, yet it is the published opinion of 

 the Messrs. Groves, that "no plants better repay a 

 little care." (Journal of Botany, 18S0.) 



The correct naming of specimens will necessarily 

 be difficult at first. For this purpose the next best 

 thing to the assistance of an expert will be the study 

 of " A Review of British Characese," by Messrs. H. 

 and J. Groves, price about two shillings, in which every 

 known British species is faithfully portrayed. In 

 cases of real difficulty there is no doubt assistance 

 would be willingly rendered, if courteously requested, 

 by some of the gentlemen whose names are on the 

 'list of " assisting naturalists " in Science-Gossip for 

 recent years. 



To recognise them in the field will require but 

 little practice. Most of them have a peculiar fetid 

 odour, and are encrusted with lime. Others are more 

 flexible, and usually less disagreeable to the sense 

 of smell. The former have the branches in whorls ; 

 the latter mostly in twos, and the branchlets forked. 

 Some of the encrusted ones show through the water 

 as patches of a greyish-green hue, from the abun- 

 dance of lime they contain. These and many other 

 interesting points will speedily manifest themselves 

 to the patient observer, who will, at least in the 

 search, find healthy recreation, if not all the scien- 

 tific success which a sanguine temperament may desire. 



Luton. 



Practical Science. — Can any reader kindly tell 

 me the name of the latest and most reliable work 

 bearing'on the above ? — Boston. 



ON THE STRUCTURE OF SOME DIATOMS 

 OCCURRING IN THE CEMENTSTEIN 

 FROM FUR IN JUTLAND. 



By MM. Prinz and Van Ermengem. 



DR. Van Ermengem read a valuable paper on the 

 above-named subject at the January meeting 

 of the Societe Beige de Microscopic A resume of 

 the same is given in No. IV. of the Bulletin des 

 Seances, 1882- 1883. The paper will appear in its 

 entirety in the Annals of the Society. 



In the hope that the subject of the resume may be 

 of interest to the diatom student, I have translated 

 it, together with the remarks of several well-known 

 Belgian diatomists. — F. K. 



The diffraction phenomena produced by structural 

 conditions of the valves of certain diatoms possessing 

 very fine markings, such as the Pleurosigmas, pre- 

 vent a very exact knowledge of their nature being 

 obtained. 



The existence of hemispherical elevations which 

 according to many diatomists produce the designs 

 is denied by others. Professor Abbe himself believes 

 that they are not due to hemispherical elevations. It 

 is very probable that all diatoms are not structurally 

 alike ; and O. Midler, A. Schmidt, and Flogel admit 

 of four or five different types. 



MM. Prinz and Van Ermengem have employed 

 in their researches species that are less delicate in 

 structure, such as Coseinodiscus oculus iridis (Eh.) and 

 Trinacria regina (Heib.), both of which are very 

 abundant in the diatomaceous rock of Fiir (Jutland). 

 In studying their valves in media possessing various 

 indices of refraction, they have obtained a succession 

 of optical reactions indicating that the valves are 

 perforated with minute openings. 



The results of their observations are entirely in 

 accordance with other methods of research, notably 

 with those obtained by the study of thin sections 

 of frustules made in various directions. The cal- 

 careous rock containing these forms admits of very 

 thin slices being cut and polished ; and these sections, 

 both transverse and oblique, allow of the diatoms 

 being studied either in the matrix or in various 

 media after the destruction of the calcite. It is easy 

 to avoid all violent manipulation that would be likely 

 to alter their structure. Mounted in a highly refracted 

 medium (1 ■ 68), 'such as saturated solution of biniodide 

 of mercury in iodide of potassium (Stephenson), they 

 give images of remarkable distinctness. We are able 

 to observe in slightly oblique sections that the valves 

 of Coseinodiscus are composed of two layers: the 

 superior layer presents the hexagonal alveolae ; the 

 inferior layer is formed of a membrane, very thin and 

 perforated by minute circular openings. The open- 

 ings are surrounded by a thick annular margin. This 

 layer when detached by the abrasion of the rock from 



