INTRODUCTION. 15 



chalk districts yield few species, although one or two 

 Desmids, such as Oosmarium iJurrciixr and ()<>< rdltnn 

 xti-fnm, have a preference for water saturated with 

 calcium carbonate. Desmids are fairly numerous on 

 some of the sandy undrained moors, but they onlv 

 Itecoine generally abundant on the older Palaeozoic 

 Rocks, or on rocks of an igneous or metamorphic 

 character. 



COLLECTION AND PRESERVATION.- -The collection of 

 material requires very little apparatus. A number of 

 corked glass tubes or wide-mouthed bottles of various 

 sizes, from about half an inch to an inch and a half in 

 diameter, will be found sufficient for most purposes. 

 A few large wide-mouthed bottles will also be useful. 

 All the bottles should bear numbered labels which 

 have been varnished, and they should lie wrapped 

 separately in paper to prevent breakage. The numbers 

 should lie entered up consecutively in a pocket-book 

 with spaces opposite each number for the description 

 of the habitat and the locality. As each bottle is filled 

 an entry should be made opposite its number in the 

 pocket-book. The bottles should not be filled more 

 than about two-thirds full, and they should be un- 

 corked immediately on arrival home. For facility in 

 moving the bottles about, they are best placed in small 

 wooden boxes about an inch in depth, and packed so 

 as to prevent upsetting. If it is desired to keep the 

 material alive for some time it mav be necessarv to 



V t-' 



transfer the contents to larger bottles, as plenty of 

 water is in most cases absolutely indispensable. 



We have already mentioned the likely places in 

 which Desmids occur, and now it remains to ive a 



O 



few hints on the collection of material. Desmids 

 sometimes occur on submerged plants in such numbers 

 that the brownish jelly in which they are embedded 

 can be gently removed from the water by means of the 

 fingers. This is, however, unusual, and submerged 

 mosses, Chara, Nitella, Gattitriche, Mynophyllum, or I 'fri- 

 cnlri, have generally to be lifted carefully out of the 



