154 PRACTICAL MICROSCOPY. 



MOSSES. These require but few instructions for collect- 

 ing. They are of little use for the purposes of scientific 

 inquiry without fruit, and therefore the collector should 

 always endeavour to procure the plant in fructification. 

 Polytrichum commune, Sphagnum squarrosum, Hypnum 

 purum, Tortula (Barbula) muralis, are amongst the more 

 common species. 



Every month produces some species to be collected ; on 

 old walls, the roofs of tiled and thatched buildings, on our 

 garden walks, on our downs and commons, on chalk and 

 sandstone, in bogs and on the mountain-top, mosses may 

 be found everywhere. The necessary apparatus for col- 

 lecting consists of an old pocket-knife, a platyscopic lens, 

 as shown in Fig. 2, a satchel or small bag, and a good 

 supply of thin envelopes, or square pieces of tissue or 

 other thin paper, in which to wrap each species. 



Books which may be consulted. Hooker, Taylor, and 

 Wilson's ' Bryologia Britannica ' ; R. Braithwaite's ' British 

 Moss Flora ' ; Stark's ' Popular History of British Mosses ' ; 

 Berkeley's ' Handbook of all British Mosses ' ; Unwin's 

 ' Dissections and Illustrations of British Mosses/ 



POLYCISTINA. These animals are a family of Rhizo- 

 poda Radiolaria, the silicious skeletons of which form a 

 series of very interesting objects for the microscope. They 

 exist on every ocean floor and embedded in rocks, fossil 

 Polycistina having been found at Oran, Bermuda, and 

 Barbadoes, as well as in many other places. The silicious 

 skeletons, or shells, as they are sometimes termed, with 

 their prolongations, are aids in discriminating between 

 Polycistina and Foraminifera, which former some of the 

 species resemble. A section of Barbadoes rock, showing 

 Polycistina in situ, is often a pretty, interesting, and in- 

 structive object. These objects may be obtained from 

 Barbadoes earth, by boiling with its own weight of washing 



