Observations on desmids from Scotland,Shetland, Cumbria and the English Midlands

Summary

Samples from bogs and lochs collected in the parish of Assynt, south — west Sutherland; loch and pool samples from Shetland; tarn samples from Cumbria and a small pool in Oadby, Leicestershire, have been examined. New desmid varieties and formae, some rare desmids and interesting observations on common desmids can be reported.     

Some Observations on Glass-Knife Making

The yield of usable knife edge per Me (for thin sectioning) was markedly increased when glass knives were made at an included angle of 55° rather than the customary 45deg;. A large number of measurements of edge check marks made with a routine light scattering method as well as observations made on a smaller number of test sections with the electron microscope indicated the superiority of 55° knives. Knives were made with both taped pliers and an LKB Knifemaker. Knives were graded by methods easily applied in any biological electron microscope laboratory. Depending on the mode of fracture, the yield of knives having more than 33% of their edges free of check marks was 30 to 100 times greater at 55° than 45°.     

Some Observations on Myocardial Revascularization

Since 1929 various surgical procedures have been devised to revascularize the ischemic heart to provide it with blood from extracoronary sources. A comparative study has been carried out in 80 mongrel dogs over a two-year period to evaluate the relative merits of cardio-omentopexy, left atrial pulmonary artery anastomosis and the Ivalon sponge operation. The Ivalon sponge procedure proved to be most effective in relieving artificially produced myocardial ischemia. The procedure has subsequently been carried out in two patients with crippling angina pectoris, and a complete relief of symptoms has been achieved in both.     

Some Observations on Attrition of Students from Canadian Medical Schools

Students who entered their freshman year for the first time in 1958 and in 1959, from all medical schools in Canada, and those entering the four Western schools in 1960 were studied from the time they matriculated until they either graduated or withdrew from medical school. The rate of attrition is about 15% of matriculants each year, with the lowest rate at the University of Western Ontario (1.7%) and the highest at the University of Ottawa (33.6%) over the time period studied. Attrition was classified as academic and non-academic. Significantly higher rates were found in the case of non-academic attrition for women and in the case of academic attrition for Commonwealth students. Significantly higher rates for both types of attrition were found for older students and students who had attended undergraduate colleges different from their medical school colleges. It would appear from available statistics that the factors which combine to produce attrition are the intellectual and personality characteristics of the student, school promotional policies and evaluation methods.     

Morphological Observations on the Exoskeletal Skull Roof of an Osteolepiform from the Carboniferous of Scotland

The morphology of the parietal shield of the Carboniferous osteolepiform Megalichthys laticeps is described. Of special note are the following features, none of which have hitherto been observed in other members of the group: each intertemporal section of the lateral-line canal system gives off a large, backwardly directed tube which enters the posterior part of the ipsilateral parietal bone where it becomes highly ramified; anterolaterally each intertemporal bone possesses an irregularly shaped and forwardly directed projection—the frontodermosphenotic process—which is traversed by the intertemporal section of the lateral-line canal system. In addition, evidence is offered that Megalichthys laticeps was equipped with a paired extratemporal bone as well as a tripartite extra-scapular series of exoskeletal elements; also, that the presence of the extratemporal bone most likely was correlated with the configuration of the subjacent part of the endocranium; and, finally, that no appreciable movement occurred between the anterior and posterior cranial divisions.     

Observations on a diatom bloom in Loch Leven, Scotland

A study was made on a freshwater planktonic population of centric diatoms, mainly Stephanodiscus rotula (Kütz.) Hendey, in Loch Leven, Kinross, Scotland. The observations were analyzed in relation to changes in water temperature and chemistry, parasitism by a chytridiaceous fungus, grazing by a recently described protozoan and competition from another alga ( Synechococcux sp.). Each of these factors is thought to have affected the recorded rise and fall in diatom population density, in particular, silica limitation, fungal parasitism and protozoan grazing.
The protozoan involved ( Asterocaelum algophilum Canter) forms digestion cysts, the predominantly diatomaceous contents of which suggested very selective feeding but laboratory experiments with dual cultures did not confirm this. They indicated that both the size and quality of algae affected their suitability as food. Feeding activities of Asterocaelum seemed to be more or less confined to a solid surface; grazing rates in cultures shaken to maintain the animals and algae in suspension were low relative to those observed in unshaken cultures. This suggests that much of the grazing occurred on diatoms that had sunk onto the sediments.     

Cytological Observations on Some Species of Dryopteris and Polystichum from China

Cytological observations on five Dryopteris species and four Polystichum species from China are reported. Most of the materials examined were field-fixed in Emei Shan, Sichuan province, and one of them was in Dali Xian, Yunnan province. Only the count of Dryopteris goeringiana was made from the plant brought from Wuling Shan, Beijing and grown in the garden of our Institute. All the materials were fixed in 1:3 acitic acidalcohol, and stained with acetocamine. All the counts were made at diakinesis or metaphase I of meiosis in SMCs .The results of the observation on them are summarized in table 1. Of these, the chromosome numbers for six species are first report. Five species are sexual: diploid: D. goeringiana, D. porosa, D. subinaequalis, D. yui and P. stenoghyllum. Three spe cies are sexual tetraploid: P. acutidens, P. erosum and P. moupingense. Only D. juxtaposita is an apomictic triploid. The vouchers are preserved in the Herbarium of our Institute (PE). We are indebted to Prof. R. C. Ching and C. R. Fraser-Jenkins for identification of the materials.