714 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Effect of Very Low Temperatures on Moist Seeds.* — T. Adams, 

 experimenting with seeds of pea, barley, flax, swede, red clover, meadow 

 feseue, and timothy, finds that whereas 6f>- ( .>6 p.c. of dry seeds ger- 

 minated after immersion in liquid air for 24 hours, a similar immersion 

 proved fatal to moist seeds. He suggests, as an explanation, a complete 

 rupture of the tissues, causing separation of the cells, or it is conceivable 

 that ice crystals may be formed inside the cell within the protoplasm 

 itself, and the death of the protoplasm may be due to mechanical effects. 

 Whatever be the explanation of what takes place, it seems fairly certain 

 that freezing to death can only occur if the seed contains more than 

 12 p.c. of moisture. He suggests that while there may be no fatal 

 minimum temperature for dry protoplasm, there is one for moist proto- 

 plasm, which lies somewhere above the temperature of liquid air. 



Movements of Petals.f — Esther P. Hensel has studied the physical 

 causes which bring about opening and closing movements, periodic or 

 otherwise, of certain flowers. A summary of the work done on the 

 subject since 1686 shows how varied have been the theories as to the 

 cause of the movement of floral leaves. The author was able to control 

 the opening and closing of dandelion heads so far as to close them per- 

 manently with lower temperature than normal, and open them when 

 temperature has continued too low, by the application of either dry or 

 moist heat. She also found it possible to close any ephemeral flower 

 before its time by an extra amount of heat, with either dry or moist air ; 

 but it was not found possible to open an ephemeral flower by placing 

 the plant in a lower temperature, since this checks growth, and opening 

 here is rather a growth movement than a stimulatory one as in other 

 types. In experimenting with dandelion, Mentzelia nuda, Ipomaa pur- 

 purea, flax, Mirabilis Jalapa, and others, light, humidity of the air, and 

 water-content of the soil, were successfully eliminated as possible physical 

 factors likely to cause the opening aud closing of flowers by the move- 

 ment of the petals or ray florets. On the other hand, heat, by its 

 variations during 24 hours, is the direct cause of movement in day- and 

 night-flowering types which bloom for more than one day. In the case 

 of ephemeral flowers which open very early in the morning like Ipomcea 

 purpurea, before the temperature has risen to any extent, or those like 

 evening primrose, which open when temperature is falling in the evening, 

 the phenomenon is less easily explained ; these, perhaps, react to a 

 smaller variation in temperature than in the case of others. 



General. 



Revised Classification of Roses. $ — J. G. Baker deals with the genus 

 by dividing it into three groups. In the first group primary species are 

 enumerated ; in the second, subspecies and varieties ; in the third, the 

 principal hybrids. The primary species are estimated as 6 { .) in number, 

 and they are classified under 11 groups, which may be briefly diagnosed 

 as follows : — I. SimpUcifolice, with simple, exstipulate leaves. II. Sys- 

 tijlm, with styles protruded beyond the disk as a united column. 



* Scientif. Proc. Roy. Dublin Soc, xi. (n.s.) pp. 1-6. 



t University Studies. Nebraska Univ., v. No. 3 (1905) pp. 1-38. 



% Journ. Linn. Soc. (Bot.) xxxvii. (1905) pp. 70-9. 



