Studies on Nitrogen Fixation by Blue-green Algae: II. NITROGEN FIXATION BY MASTIGOCLADUS LAMINOSUS COHN

Mastigocladus laminosus Cohn, a blue-green alga of hot springs,has been obtained in pure bacteria-free culture and has beenshown to be capable of fixing elementary nitrogen. This appearsto be the first instance in which this capacity has been demonstratedin a blue-green alga belonging to a family other than the Nostocaceae.     

The penetration of 3:5-dinitro-o-cresol into leaves

A study of the penetration of 3:5-dinitro- 0 -cresol from spray solutions or suspensions into leaves of Sinapis arvensis L. shows that entry through the stomata is unimportant. Lethal amounts may enter from aqueous solution by simple diffusion of the undissociated phenol through the epidermis, which behaves as a homogeneous lipide membrane. The effect of the structure of the epidermal surface on the rate of diffusion is discussed. Lethal amounts may also enter Sinapis from a dry surface deposit by gaseous diffusion through the stomata or by diffusive penetration of the epidermis following sublimation. Movement of the substance within a plant is slight and appears to be mainly by diffusion. The selective action of 3:5-dinitro- 0 -cresol as a weed-killer is discussed in the light of these results.     

Growth and Heterocyst Production in Anabaena cylindrica Lemm: III. The Cytology of Heterocysts

A study has been made of the cytology of the heterocysts ofAnabaena cylindrica Lemm. at different stages during the growthof this alga in culture. The techniques used include that ofFeulgen, a modified Sakaguchi test for arginine derivatives,ultra-violet photomicrography, and micro-incineration. It hasbeen shown that the formation of a heterocyst begins with themobilization of material so that its protoplasm becomes homogeneous.The protoplast eubquently becomes depleted of all materialademonstrable by the methods used. At intermediate stages indevelopment substances become concentrated near the connexionsof the heterocyst and a central transverse zone, retaining materiallonger than the reat of the protoplasm, becomes apparent. Thestructure and development of heterocysts is discussed.     

The Kinetics of Extracellular Glycollate Production by Chlorella pyrenoidosa

Extracellular glycollate is liberated by Chlorella pyrenoidosaduring growth in medium bubbled with air or 3 per cent carbondioxide in air. With air the rate of release of glycollate percell decreases, with 3 per cent carbon dioxide it increases,with increase in cell number. Glycollate is released duringshort-term experiments when C. pyrenoidasa, grown under lowlight and high carbon dioxide, is transferred suddenly to highlight and low carbon dioxide. No other combination of thesefactors produces a comparable release of glycollate. The quantityof glycollate released in short-term experiments increases exponentiallywith the relative growth-rate of the culture from which thecells are derived. A crucial condition for maximum glycollaterelease is that growth of the culture prior to the experimentshould not be limited by carbon-dixoide concentration. The effectof pH is related to its effect on growth-rate; i.e. C. pyrenoidosahas a lower relative growth-rate at pH 8.3 and produces correspondinglyless glycollate than faster growing cultures at pH 6.4. Duringshort-term experiments under high light and low carbon dioxidethe rate of glycollate release drops after 50–100 minutessuggesting exhaustion of the glycollate precursor.