258 



HARDWICKE'S SCIENCE-GOSSIP. 



The skeleton of the second example is preserved in 

 the Liverpool Museum. — H. J. Torpey. 



Veronica cham.-edrys. — The grub mentioned 

 by your correspondent Mr. Woodruffe Peacock as 

 causing a distortion of the upper leaves of this plant 

 is no doubt that of Cecidomyia Verotticce. See Frank's 

 Pflanzenkrankheiten, (Schemks' Ilandbuch der Bo- 

 tanik, vol. i. p. 547). The insect is a near relation 

 of the Hessian fly {Cecidotnya destructor) and of 

 the wheat midge [C. tritici), both of which are fully 

 described in Miss Ormerod's " Manual of Injurious 

 Insects."—/?. //. Scott. 



MICROSCOPY. 



On the Supposed Discovery of Pseudopodia 

 IN Diatoms. — We are much pleased to insert the fol- 

 lowing paper, by Mr. G. H. Bryan (an old contributor, 

 but youthful and promising scientist) from the " Inter- 

 national Journal of Microscopy, &c. " : — At the recent 

 meeting of the British Association in Cardiff, Mr. J. 

 G. Grenfell read a paper " On some species of Dia- 

 toms with Pseudopodia," in which he announced 

 that the pseudopodia of diatoms have at last been 

 observed. The species on which they were dis. 

 covered belong not to the motile, but to the fixed 

 forms, being of the genera Melosira and Cyclotella. 

 The discovery was made at an excursion of the Que- 

 kett Club to the Botanical Gardens, Regent's Park, 

 where Mr. Grenfell found the diatoms swarming all 

 over the surface of one of the ornamental pieces of 

 water, forming quite a little cloud of a nearly pure 

 gathering. At a subsequent visit he was unable to 

 obtain such pure gatherings, but the diatoms were 

 still present, and he collected a quantity of material 

 for future observations. The pseudopodia were seen 

 under a Jth object-glass, and nearly all belonged to a 

 small kind of Melosira, whose frustules were mostly 

 simply united in pairs, though they sometimes formed 

 short chains. The frustules of this diatom were very 

 soft and hardly at all siliceous, and they were de- 

 stroyed :by boiling in acid. Mr. Kitton thought the 

 diatoms were a variety of Melosira variaiis, but Mr. 

 Grove had never seen pseudopodia attached to M. 

 varians, and doubted their belonging to that species. 

 At the second visit, Cyclotella Kiitziii^ana was found 

 abundantly in the locality in question, with pseudo- 

 podia attached. Mr. Grenfell afterwards found dia- 

 toms with pseudopodia at Stanstead in Hertfordshire, 

 and at Westbury in \Yiltshire he found many of the 

 streams swarming with a delicate Melosira, which 

 was covered with pseudopodia. Probably, further 

 observations will shov/ that such diatoms are by no 

 means uncommon, and that they are widely dis- 

 tributed over the country. The pseudopodia are 

 quite invisible when the diatoms are immersed in 

 water, and the best way of seeing them is to dry the 



diatoms by allowing the water containing them to 

 evaporate gently on the cover. The appendages . 

 will then be seen spreading out in all directions, 

 often thickly matted together. They may be stained 

 with an aqueous solution of gentian violet, with 

 methyline blue, or with fuchsine. A solution of 

 borax-carmine stains the bases only, while alcoholic 

 stains fail altogether. After staining, the diatoms 

 may be mounted in balsam. In no case were the 

 pseudopodia seen to move ; they appeared to be stiff 

 and non-contractile. They are arranged fairly sym- 

 metrically round the frustule, their number being, 

 usually from seventeen to twenty, though occasionally, 

 as ;in the genus Cyclotella, there are as many as 

 thirty-four pseudopodia, arranged with remarkable 

 regularity. The pseudopodia are usually perfectly 

 straight, but sometimes they are branched. Some- 

 times their surface is beaded or granular, and some- 

 times they are quite thick and even slightly siliceous- 

 at the base, but in all cases they were found to be 

 destroyed by heat. They always seem to spring from 

 the large markings on the frustule, but sometimes two 

 pseudopodia seemed able to fuse into one another. 

 The frustules were generally united in two's and 

 rarely in longer filaments. Mr. Grenfell supposed 

 that the pseudopodia have three uses : they serve as 

 protections, as floats to sustain the diatom, and for 

 the purpose of attaching it to other objects. The 

 author did not think that they bear any analogy to- 

 the processes of Chretoceros. Mr. Grove had sug- 

 gested that the pseudopodia were simply extensions 

 of a ^gelatinous investing layer, but Mr. Grenfell 

 doubts this. It might also be thought that the ap- 

 pearance was due to some rhizopod, such as a Vam- 

 brella, investing the diatom, but such cannot be the 

 case. Over two hundred frustules of Melosira, all fur- 

 nished with pseudopodia, were found in one dip of the 

 material, and in no case did Mr. Grenfell see any trace 

 of an investing animalcule. Moreover, such an animal- 

 cule would very rapidly kill and devour the diatom, 

 whereas Mr. Grenfell found that the diatoms re- 

 mained alive for a considerable time. The author 

 also pointed out that if the pseudopodia belonged to 

 an investing organism, it would be highly impro- 

 bable that they would be distributed symmetrically 

 round the frustule. The pseudopodia bear consider- 

 able resemblance to those of certain heliozoa, such 

 as Archerina Boltoni. This animalcule occurred ,in 

 abundance in the later gatherings which Mr. Grenfell 

 made at the Regent's Park ; and it was not improb- 

 able that the diatoms might occasionally be mistaken, 

 for rhizopods, especially where both were found in 

 the same gathering. The remarkable similarity 

 between the pseudopodia of Melosira and Cyclotella 

 and those of Archerina, when considered in con- 

 junction with the presence of cellulose in Arche- 

 rina, would seem to indicate a greater affinity 

 than that already known to ' exist between, 

 the more lowly forms of the animal and vege- 



