Staurastrum gracile Ralfs. was grown in Chu’s No. 10 culture medium, in a culture cabinet at 18–20°C with 16 hrs light and 8 hrs dark period. The cells exhibited polymorphism. The cells were fixed and their division and growth was examined under the scanning electron microscope.

A detailed study of surface ornamentation under light and scanning electron microscope is undertaken. The present observations have added further to the knowledge in taxonomic identification ofCosmarium botrytis Menegh, in particular because the species revealed a variety of surface ornamentation based on which various species ofCosmarium are specifically identified.

Various species of desmids (Cylindrocystis brebisonii, Closterium acerosum, closterium littorale, Cosmarium bioculatum, Cosmarium botrytis, Cosmarium contractum andCosmarium subtumidum) were studied for their surface ornamentation. After trying various methods for removal of the mucilage, it was found that pretreatment with the glusulase preparation was usually effective in cleaning the cells and enhancing their appearance under theSem.

The variability of the desmids was quite interesting to note that when the conditions such as temperature and illumination were altered, there was not only an increase in the abnormal forms but the number of the adherent cells were also more. This abnormal behaviour of the species was more or less directly proportionate to the altered status of these factors in culture. It was thus quite clear that due to an increase or decrease in temperature and light intensity, quite a number of variants were produced. Sometimes the cells departed so widely from the specific characteristic that one could mistake them as belonging to different taxa. It may be that under unfavourable conditions of growth the mechanism of cell division was disturbed lowering thereby the percentage of mitosis and finally leading to the tendency of morphological aberrations. Consequently, these observations induced to study the various species of desmids under different experimental conditions to find out the range of morphological variation in cultures because the feature which more than any other, has attracted algologists to study desmids especially placoderms is their considerable morphological variability. Morphological variations under different cultural conditions have been studied and it is presumed that the cell types are capable of maintaining their narrow specificity, which is genetically controlled under favourable conditions only, but, whenever, there is a change in environmental set-up, it has resulted in upsetting the metabolic behaviour leading to abnormal forms.