HARDWICKE'S SCIENCE- GOSSIP. 



IS 



The Isoetes are there classed in three divisions. 

 Eirst, the Aqvaticce, which include the I. lacustris 

 only. Secondly, the Palustres, comprising I. tenuis- 



only scales, therefore if not the I. Buricei (or a sub- 

 species), must be a distinct species. The I. Buricei 

 taken in Algiers is very large in comparison with 

 the Guernsey plant, from growing in a pure, soft, 

 sandy soil, allowing the bulb to expand. The- 



Fig. S. Isoetes Duriai. 



sima, Boreau, 1. adspersa, Braun (Perreymondi, 

 Bory), and I. setacea, Delille. Thirdly, Tejrestres, 

 comprising /. Hystrix, Bory, Durieu, and Cosson, 

 and 1. Durieu, Bory. 



The Aquatics have no scales (phyllopodes) ; the 

 Palustres also have no scales ; the Terrestres have 

 the rhizome covered with persistent scales. The 

 7. Hystrix has the bulb surrounded by short, black 

 shining scales, terminated by two long linear subulate 

 horns (spines), between which often appears a third, 

 very short. The I. Buricei, Bory, has the bulb also 

 surrounded by scales, only very short, black, largely 

 truncated, and shortly tridentate (no spines). The 

 distinctions are thus clearly defined, showing that 

 no species that has not the spines can be the Hystrix. 

 The Guernsey plants sent to me have no spines, 



Fig. g. Isoetes Darixi (Guernsey plant). 



specimens from which the illustrations are taken 

 agree with the foregoing respective descriptions. 

 Brighton. T. B. W. 



CEMENT EOR DRY-MOUNTING MICRO- 

 SCOPIC OBJECTS. 



THE very frequent occurrence of slides becom- 

 ing defective, either through the covers or 

 cells coming off or from the cement running in or 

 letting in the air, induced me about a year and a 

 half ago to send a communication to the editor of 

 Science-Gossip on the subject (and which appears 

 at p. 131 of the volume for 1874), intending to give 

 the results of many years' experience by stating 

 what I had found to be the most reliable materials ; 

 but illness occurring, prevented its completion 

 at the time, and being followed by disinclination 

 and want of energy, this led to its protracted post- 

 ponement. In that paper I stated my aversion to 

 the use of gold size, as a most objectionable 

 element, from its tendency to run in, owing to its 

 not hardening throughout, but only on its exterior 

 surface ; and at the same time making allusion to 

 a new material which bid fair to be of great value 

 as a substitute ; and, fortunately, the time which has 

 now elapsed enables me to confirm most fully the 

 favourable opinion originally formed as to its merits. 

 This varnish was first introduced to my notice by 

 Mr. Ackland, as his colourless cement for fixing covers, 

 &c. ; and immediately on its composition being- 

 imparted to me in confidence, I at once recognized 

 its importance in the place of gold size, and having 

 prepared some liquid asphalt with this varnish, in 

 lieu of the gold size, I set to work to.test its appii- 



