376 Physiologie. 



gestellte Pflanzen erfrieren weniger leicht als solche, die im Warm- 

 hause gestanden. Die Pflanzen sind aber auch im Stande, sich selbst 

 zu schützen, und zwar durch die Gefrierpunktserniedrigung, die 

 durch Concentrierung des Zellsaftes eintritt. So findet nach Lid- 

 fors im Herbste eine Ueberführung der Stärke in Zucker bei 

 unsern wintergrünen Bäumen statt, dieser Zucker setzt den Gefrier- 

 punkt bedeutend herab und erhöht dadurch die Kälteresistenz. 



G. V. Ubisch (Berlin). 



Petersen, C. G. J., Om Baendeltangens {Zostera marina) Aars- 

 Produktion i de danske Farvande. [On the yearly produc- 

 tion of Zostera in Danish waters]. (Mindeskrift for Japetus 

 Steenstrup. IX. p. 1—20. 1 fig. 8 tab. and an english summary. 

 Köbenhavn. 1913.) 



By studying the nodes of the rhizome the writer flnds that each 

 shoot generally produces ca. 10 leaves and rhizomenodes during 

 the summer and ca. 5 during the winter, The nodes are generally 

 Short in winter and long in the good time of the ye^r, thus long 

 rhizomes show alternate series of long nodes and short nodes. As 

 a rule each shoot has only ca. 5 leaves at one time, the older ones 

 having fallen of. Therefore the Zostera- vaass (with 5 leaves pr. shoot) 

 growing in summer on 1 m^ of bottom represents about one half of 

 the leaf production during the summer. 



The maximum quantity of Zostera leaves per 1 m- was found 

 at favourable places to be 6000 gms., at moderately good places 

 3500 gms. and at bad places 1700 gms. By doubling these numbers 

 we get 12000, 7000, and 3400 gms. as the total yearly production, 

 thus paying no attention to the production in winter nor to the 

 occurrence of roots. 



The dry-matter percentage of Zostera being ab. 16 the yearly 

 production of dry-matter pr. 1 m^ is 1920, 1120, and 544 gms. 



Taking the average yearly production as 1200 gms. dry-matter 

 the total production of ca. 2000 square sea-miles of Zostera in danish 

 waters amounts to about 8232 million kg. 



This considerable production when decayed has economical 

 importance as food for lower animals which are again eaten by 

 fishes. The writer points out that more could be done in order to 

 make use of Zostera. Ove Paulsen (Copenhagen). 



Petrie, J. M., Hydrocyanic Acid in Plant s. Part II. Its 

 Distribution in the Grasses of New South Wales. (Linn. 

 Soc. N. S. Wales Abstr. Proc. p. IV. Oct. 29th 1913.) 



The existence of hydrocyanic acid in the Gramineae was disco- 

 vered by Jorissen, in 1884. Since then, about 30 species have 

 been recorded as containing a cyanogenetic Compound, and among 

 these are the sorghums, well known for their poisonous properties. 

 The author's work is a continuation of some investigations into the 

 cause of sudden fatalities among sheep in this State. Over 200 spe- 

 cies of grasses were systematically tested at different seasons. These 

 were growing wild, or cultivated in the Botanical Gardens and 

 Experimental Farms. Glucosides, capable of yielding hydrocyanic 

 acid, were detected in 20 species, 11 of these being native grasses, 

 the others introduced. The positive reactions have been confirmed 

 in specimens from different localities. The seasonal variations are 



