346 



KNOWLEDGE. 



September, 1912. 



is yellow; whiK' lli.il of llic long ones is bluish-grccn. In 

 some c.'iscs the ki'^'iks of poilcii liavc niiincroiis thre.'icls, 

 probably of iniicil.iKe — formed from (lie outer wall. 



.•\s already mentioned, by far the most common form of 

 pollen is elliptical, with three ribs. For this no explanation, 

 he believed, has yet been sugfiested. Snch pollen was 

 oriRinally spherical, and only assumed the elliptical three- 

 ribbed form .ifler leaving the anthers and losing a certain 

 amount of moisture by desiccation. Fairbairn in his " Useful 

 Information for Kngineers " describes how tubes give way 

 under pressure. They collapse at three c(|ui-distant points, 

 thus assuming a three-lobed form. Lord Avebury suggested 

 that the three-lobed form of most pollen was perhaps due to 

 the same cause, and did not present any advantage in itself. 

 At the same time the extiiie was in many cases thinner in the 

 furrows. This, he thought, was perhaps explainable as being 

 due to inheritance. He suggested that the dumb-bell form 

 was due to the fact of the furrows being shorter and deeper in 

 the middle. 



It was interesting to compare the form of the pollen when 

 the order contained both anemophilous and entomophilous 

 species. For instance, Conipositae for the most part have 

 spiny pollen and are entomophilous, but the Edelweiss and 

 some allied species are anemophilous and smooth. The 

 Rosaceae are almost all entomophilous, with elliptical pollen, 

 but Poteriiim is anemophilous with spherical pollen. A good 

 case is afforded by the Salicaceae; the willow is entomophilous, 

 with elliptic three-ribbed pollen. The Poplars, on the contrary, 

 are anemophilous with spherical pollen. 



He then discussed the size of pollen, and referred to a long 

 table which he thought afforded conclusive evidence that, 

 though the size of the pollen did not depend entirely on the 

 pistil, and the length, therefore, which the pollen tube had to 

 traverse, still as a general rule, the longer the pistil the larger 

 the pollen. The genus Mirabilis affords a very interesting 

 illustration. It had been long ago noticed by Kolreuter that 

 M. jalapa can be fertilized by the pollen of M. longifolia, but 

 that M. longifolia cannot be fertilized by M. jalapa. 



No explanation of this curious fact had. so far as he knew, 

 hitherto been suggested. He submitted that it was probably 

 due to the relative size of the pollen and length of the pistil — 

 the pollen of .17. loitgifalia being considerably larger than that 

 of M. jalapa; so that the pollen tube of iVf. /o«gi/o7;rt can 

 reach the pistil of both species, while that of M. jalapa. 

 though large enough for tlie pistil of its own species, is unable 

 to reach those of M. longifolia. He concluded his memoir 

 with a description of the pollen in the principal British orders. 



A paper " On Some New Astrorhizidaeand their Structure " 

 was contributed by Messrs. E. Heron-Allen and Arthur 

 Earland. Two new' species of Psaiuinosphacra and one of 

 Marsipella were described from specimens dredged by Mr. 

 Earland in the North Sea in connection with the work of the 

 International North Sea Investigations (Scotland). 



In Psaminosphacra rustica the rhizopod constructs a 

 polyhedral test of spicular fragments selected of suitable 

 length and cemented side by side in a single layer, while in 

 Psammosphacra Boic'iiiani large Hakes of mica are selected, 

 and cemented together at the edges so as to form a polyhedral 

 test. Marsipella spiralis constructs a straight tube of 

 minute spicular fragments of approximately equal length, 

 which are embedded, side by side, in a fine grey cement. 

 The spicules are arranged in definite rows which run in a 

 sinistral spiral round the tube. 



The authors also dealt at some length with the minute 

 structure of Technitclla Icgnmcn Norman and Marsipella 

 cylindrica Brady and described some hitherto unrecorded 

 details of the construction of the tests in these species. 



Dr. J. F. Gaskell communicated " A method of embedding 

 tissues in Gelatin." The tissue is fixed in a formalin mixture; 

 previous to embedding ;ill formalin must be removed by 

 washing in running water twelve to twenty-four hours. The 

 gelatin is soaked for three to four minutes in cold water, then 

 drained and melted, and the tissue is immersed in this for two 

 to five hours in an incubator <at 37° C. It is then cast in 

 paper boxes in this gelatin and allowed to set at room temper- 

 ature; when cool, it is put into a formalin vapour chamber to 



harden. The hardening is not satisfactory in a less period 

 than three days, and may be continued indefinitely till the 

 block is wanted. 



Sections are cut by the freezing method, the block being 

 pared down and attached to the st.'ige of AschofTs COj 

 freezing microtome by means of a drop of gum solution. 



Sections can be obtained of any tissue 10m thick and of 

 most tissues hitherto tried 5^ sections are obtainable. 



gUICKETT MICROSCOPICAL CLUB.— On June 25th, 

 1912, Mr. \V. B. Stokes (the honorary secretary) read a paper on 

 " Resolutions obtained with dark-ground illumination and 

 their relation to the ' spectrum ' theory." Serious students of 

 microscopical images have long sought a crucial experiment 

 which shall decide the claims of the two theories, those of 

 Airy and Abbe, which have been put forward to explain them. 

 The image obtained by dark-ground illumination offers the 

 very example sought. If the Abbe spectrum theory is to be 

 applied, it will be necessary for maximum resolution that a 

 spectrum of the second order be included in the objective to 

 cooperate with that of the first order, each spectrum just 

 entering the objective on opposite sides. It was then shown, 

 using the usual formula, that an objective of N. A. 1-0 and 

 illuminator of N.A. 1'35 would resolve 58,750 lines per inch 

 at X 5080. It was found, however, in practice, that an 

 objective of N.A. 0-86 with illuminator of N..-\. 1-35 would 

 resolve the 60,000 band of a Grayson ruling, and also the 

 Cherryfield Naviciila rhomboidcs. believed to have rows of 

 perforations 60,000 to the inch. These results and others 

 quoted would seem to show that we are justified in turning to 

 the older (Airy) theory for guidance. 



Mr. A. E. Conrady, F.R..-\.S., said the formula quoted for 

 resolving limit applied to a grating absolutely uniform in ruling 

 and one which had also an infinite number of lines. When a 

 grating has a limited number of lines it becomes easier to 

 resolve. Grayson's thirty lines at sixty thousand is in this way 

 subject to a discount of about three per cent. The coarsest 

 line in a group of rulings will influence the resolution of that 

 group. 



Mr. R. W". H. Row, B.Sc, reported the occurrence, at 

 Maiden railway station, Surrey, and showed specimens, of a 

 rare saw-fly. Phyllotnina Uineris ? ). 



ORNITHOLOGY. 



THE GREAT REED WARBLER.— Mr. E. C. Taylor 

 writes from Yarmouth as follows : — " Your Ornithological 

 readers may be interested to learn that the Great Reed (or 

 Sedge) Warbler iAcrocephalus tiirdoides) was seen by me on 

 Sunday last between Horning Ferry ;ind Ranworth. I should 

 consider that the bird being here at this time of the year 

 makes it very probable that it has been breeding here. 



I was on an entomological hunt by the side of a reed bed 

 near a small " corr " when my attention was drawn by a bird 

 of unusual size flying in and out of the reeds. It settled on 

 the stem of a reed quite near me and I had a good view of it 

 for quite thirty seconds and am certain of its identity." 



"BRITISH BIRDS."— In the August number of British 

 Birds there are as usual a number of very interesting notes. 

 Mr. P. F. Bunyard records some of the earliest nests which 

 he found in 1912. He thinks that May 1st for the Bl.ackcap 

 in Kent, and May 4th for the Lesser Whitethroat in Surrey 

 may be new records. Mr. Jourdain, in an editorial note, how- 

 ever, gives .April 28th for the latter bird on the authority of 

 Mr. J. E. Harting, who states that an egg was found in 

 Willesden on that d.ate. Mr. Buny.ird also found a Cuckoo's 

 egg in Kent on May 6th, which is a fortnight earlier than any 

 of his own previous records. A second specimen of the 

 Is.abelline Wheatear, Mr. Thomas Parkin records, has been 

 shot in Sussex, which is apparently only the fourth specimen 

 obtained in this country. It has been secured by Mr. W. H. 

 Mullens, who has presented it to the Hastings Museum as an 

 addition to the fine collection of local birds already given by 

 him to that institution. 



