204 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Nitrates and the Carbon-Assimilation of Algae.* — A. E. N. Arber 

 Las continued his experiments on the effect of salts on the carbon- 

 assimilation of TJlva latissima and other green sea-weeds. He finds that 

 the addition of a nitrate to sea-water causes an inhibition of the carbon- 

 assimilatioi:, the extent of which varies with the nature of the base. 

 Thus the presence of ammonium nitrate quickly proves fatal, while 

 potassium nitrate has a greater effect than sodium nitrate. The addition 

 of magnesium nitrate, which is normally present in sea-water, causes the 

 least marked inhibition. He also finds that tiie presence of an appre- 

 ciable quantity of potassium jmosphate causes considerable inhibition. 



Germinating Power of the Seeds of Cereals.j — Dr. A. Burgerstein 

 has made a further observation on the power of seeds to retain their 

 germinating power under favourable circumstances. He found that 

 grains of maize lost their power of germinating after 10, those of 

 v.heat after 15 years ; while after this latter period 75 p.c. of grains 

 of barley and oat germinated and produced normal plants. 



"Ageing" of the Embryo of Grasses.^ — E. Gain has continued his 

 observation on the grains of a variety of cereals obtained from Egyptian 

 mummies. The changes which take place during long periods in the 

 embryo, and which are either the cause or the result of its loss of 

 vitality, are indicated by a gradually deepening brown tint ; and the 

 depth of this colour is a rough indication of the age of the grain. 



Irritability. 



Position of Flowers with respect to Light.§ — Prof. J. Wiesner 

 points out that flowers are governed by the same laws as leaves in 

 respect to their exposure to light. The formation of flowers especially 

 on the side facing the light, is not necessarily the result of heliotropism, 

 but may be a phenomenon of phototrophy , i.e. the stronger development 

 of organs or of tissues on the more strongly illuminated side, in plants 

 which are unequally illuminated on different sides. Phototrophic bowers 

 are hence contrasted with photometric ; though the object is the same 

 in both cases, viz. to render the flowers as accessible as possible to visit- 

 ing insects. Leaves are euphotometric, i.e. are so placed as to receive 

 the greatest possible amount of light, when the plane of the blade is 

 vertical to the direction of the strongest diffused daylight ; in euphoto- 

 metric flowers, the opening of the flower is vertical to the direction 

 of greatest illumination. A good example is furnished by Ipomsea 

 purpurea. 



Resistance of Seeds to Low Temperatures. || — Experiments by 

 A. D. Selby confirm the results arrived at by Thiselton-Dyer and others. 

 With the seeds of a number of different plants, immersed for periods 

 varying from 3 to 28 days in liquid air (— 190° C), some suddenly, 

 some gradually, it was not apparent that any marked unfavourable effect 

 on their germination could be traced to their immersion. 



* Ann. Bot., xv. (1901) pp. 669-81. 



t Verhandl. k. k. Zool.-bot. Ges. Wien, li. (1901) pp. 645-7. 



X Comptes Rendus. cxxxiii. (1901) pp. 1248-50. Cf. this Journal, 1900, p. 640. 



§ Biol. Centralbl., xxi. (1901) pp. S01-14. Cf. this Journal, 1899, p. 599. 



|| Bull. Torrey Bot. Club, xxviii. (1901) pp. 675-9. Cf. this Journal, 1900, p. 84. 



