SCIENCE- GOSSIP. 



79 



•crescent-shaped outline is sufficient to distinguish 

 at once most of the species of Closterkvm. Speci- 

 mens of the genus are common in ponds and ditches, 

 and are by no means confined to mountain peat 

 bogs. Ponds in the neighbourhood of London are 

 known in some seasons to yield quantities of them ; 

 and the specimens figured were taken from roadside 

 runnels, the gathering of C. striolatv/m forming- 

 dense green patches. The large C. lunula or the 

 C. costatum figured in the April issue, or one of 

 the other larger species form an interesting and 

 fascinating study in the living state. At the tip 

 of either " horn " is a spherical cavity containing 

 a number of tiny granules in active movement. 

 These exist in all the species of the genus, though 

 they can best be seen with a moderate power in 

 the larger forms. I have, however, slides contain- 

 ing two small species, Closterium moniliforine, and 

 the slender G. rostratum, whose fronds terminate 

 in sharp beaks. These desmids were collected 

 from a ditch on the way to Aber waterfall, and in 

 spite of their having been mounted in glycerine 

 for about a year it is easy to find specimens in the 

 mounts in which the granules have retained their 

 position, and are to be distinctly seen with a half- 

 inch, or even with an inch objective. Another 

 feature is the circulation of the cell-contents. 

 The process of reproduction by subdivision has 

 already been described in a paper in the New 

 Series of Science-Gossip, and in gatherings where 

 the desmids are abundant specimens in different 

 stages of subdivision are readily found. Mr. Noad 

 Clarke in his photograph of C. costatum on page 325 

 has succeeded in including one specimen shortly 

 after subdivision, in which the newly formed half 

 of the frond has not nearly reached its full size. 

 Keproduction by conjugation is much less fre- 

 quently met with, and specimens in this state 

 should therefore, if found, be carefully preserved. 



Next to C'losterium comes Penium, a genus con- 

 taining, according to Dr. Cooke, nineteen British 

 species, independently of varieties. These all have 

 a simple oval or oblong outline without any irregu- 

 larities (fig. 1) ; in a few examples the frond is 

 slightly narrowed at the middle, but there is no 

 constriction. The length of the frond is from 

 twice to eight times the breadth ; and the elongated 

 shape, resembling that of diatoms of the genus 

 Piunularia, should suffice to identify some of the 

 commoner kinds, which have, in fact, a very or- 

 dinary appearance. The specimens from which 

 the photograph was taken are from a Sphagnum 

 bog between Port Dinorwic and Pentir in North 

 Wales, where at suitable seasons they appear to be 

 extremely abundant. Some of the individuals 

 have undergone slight contraction, but this was 

 owing to the material being left standing for some 

 days in a bottle of water before being dealt with, 

 and it did not occur during the process of preparing 

 and mounting. In these, the cell-contents are 

 seen to separate into two parts, the nucleus being 



in the centre of the bridge conned in^ t hem. Many 

 of the desmids on this slide contain one or 

 more large brown globular bodies, covered with 

 fine setae; these cannot, of course, be spores, and 

 it is difficult to imagine what they can be, unless 

 they are parasitic. Careful focussing shows them 

 to be inside the desmids. 



The genus Tetmemorw contains four British 

 species, one of which is figured a I BB in the group on 

 page 257 of Science-Gossip for February. They 

 are all of much the same shape, and the genus is 

 distinguished from Penium by the constrictions at 

 the middle of the fronds, the ends also having 

 an acute incision. The species is common in 

 Sphagnum washings up the Ogwen Valley. 



Two other genera, Culindrocystis containing 

 two species, and Mesotaenium containing three 

 British species, have shortly oval or cylindrical 

 cells with rounded ends, and without constriction, 

 about twice as long as broad. 



The last of the smooth-spored genera is Spiro- 

 taenia, which can be at once distinguished from all 



Pia. 1. Penium digitus, with one Mkrasterias crenaia. 



other desmids by the spiral arrangement of the 

 chlorophyll ; the cells are oval and enclosed in a 

 thick gelatinous envelope. One of these, S. con- 

 densata, occurs in some gatherings from the moun- 

 tain bogs near here, but as yet I have found it 

 sparingly. 



Passing on to the rough-spored genera, the mem- 

 bers of the genus Mierasterias claim attention as 

 including by far the most attractive and beautiful 

 of all the British desmids. 31. oseitcms (fig. 2) is a 

 representative form of the sub-genus Tetrachagtrvmi . 

 containing three British forms, while the typical 

 genus, or Emnicrasterias, is represented by 31. 

 rotata in vol. vi. p. 257. tigs. 1 and 2. 31. jetmeri 

 (fig. 3 below) and 31. crenata (in fig. 1). Pig. 9 shows 

 a group of desmids obtained last summer from a 

 ditch containing SpJiaffnum on the old road from 

 Bethesda to Ogwen, and well illustrates what 

 clean gatherings can be obtained by the method of 



