584 Varietäten etc. — Physiologie. 



erst bei Schlag oder Druck ungefähr dort ab, wo sie bei den Stamm- 

 formen sich von selbst ablöst. Ausserdem sind bei den Stammformen 

 die Deckspelzen im unteren Teile und die Aehrchenachsen dicht 

 mit ziemlich langen geraden Haaren bedeckt, bei den Saathafer- 

 formen sind diese Teile wenig behaart oder was die Deckspelzen 

 betrifft ganz unbehaart. Die Gruppierung und die Verbreitung der 

 oben genannten 4 Stammformen ist genau angegeben. Sie zeigt 

 folgendes: A. sativa und A. orientalis sind wohl aus zwei verschie- 

 denen Formen von A. Jatua in verschiedenen Gegenden des west- 

 lichen Zentralasiens in der Kultur hervorgegangen. Die Av.tiuda- 

 Formen sind erst aus A. sativa und A. orientalis entstanden; als 

 konstant gewordene Missbildungen dieser Gruppen sind sie anzusehen. 



Matouschek (Wien). 



Blaauw, A. H., De primaire photogroeireactie en de 

 oorzaak der positieve krommingen van Phycornyces nitens. 

 [The prima ry photo-growthreaction and the cause of 

 the positive phototropism in Phycornyces nitens.] (V^rsl. 

 kon. Ak Wet. Amsterdam, 27 December, 1913.) 



It seemed desirable to the writer to pass no further judgment 

 as to the value and meaning of curvature reaction until further 

 jnquiry had been made into the way in which a growing organ acts 

 when light warmth etc. act in definite quantity on that organ 

 uniformly from all sides. In the first place the Phycornyces was 

 chosea to entrace the influence of light on a Single cell viz the spo- 

 rangiophore, when 3—4 cm. Illuminated on each of the 8 sides with 

 14 M. candle during 15 sec. the result is: 



r^. that immediately after Illumination growth still remains the 

 same for about 3 min. 



2'K that after about 3 min., growth at once markedly increases 

 to reach a maximum 4| tot 8 min. after illumination: with this 

 quantity of light the maximum is usually not less than 2 or 3 times 

 the normal rate. 



30. that afterwards the rate of growth again diminishes to iis 

 normal after 7 — 16 min.; but often the rate sinks to 10— 30 '^/o below 

 the normal value for some minutes and then later becomes quite 

 normal again. 



This reaction of growth to light is named primary photo-growth 

 reaction; in this case a positive one, completely at variance with the 

 general opinion, which says that light exercises in general an retar- 

 ding influence. These former conceptions are caused by various 

 facts; that very large quantities of light were used, which greatly 

 exceeded the optimum, that the illumination was very prolonged, 

 and frequently intermitted, finally because observations were made 

 at too great intervals, so that the values were lost in an average 

 value. In the case of unilateral illumination of Phycornyces the po- 

 sitive curvature never appears, unless the above described accele- 

 ration of growth has previously taken place. 



After the meaning of the writer the proofs have been furnished 

 that the appearanec of these curvatures of Phycornyces is the result 

 of an asymmetrical modification of the growth of different sides of 

 the cell, caused by the asymmetrical illumination on these sides. 

 The rays which practically run parallel fall on the sporangiophores 

 as on a cylindrical lens and are concentrated on the posterior side. 

 The growth of this side is by weak unilateral illumination acce- 



