ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 629 



unicellular organs like Vaucheria, Mueor, and the root-hairs of 

 Marchantia, are not due to changes in the turgidity, but to variation 

 in the growth of the cell-wall. 



Movements of Tendrils.* — H. de Vries has applied to the 

 determination of the cause of the movements of tendrils the plan of 

 injection of water proposed by Dutrochet, the air of the intercellular 

 spaces being fii'st removed by the air-pump and then replaced by 

 water. The plants experimented on were Sicyos angulatus, Cucurhita 

 Pepo, and EcMnocystis Idbatd, and the general conclusions arrived at 

 were as follows : — 



1. All the movements of tendrils are temporarily increased by the 

 injection of water, the only exception being the retrograde movement 

 which takes place after the removal of the support. 



2. Straight tendrils, when not irritated, remain straight after in- 

 jection with water. 



3. The acceleration is much more considerable in the case of 

 irritable than of epinastic movements ; after a short irritation tendrils 

 attain a much greater degree of curvature than would be possible, 

 in the same conditions, without injection. 



As I'egards the cause of the movements, the author considers it to 

 be proved that 



4. The force of turgidity in the parenchyma of the tendrils at 

 the time of the epinastic straightening, and subsequently at the time 

 of the epinastic unrolling, is partially inactive. 



5. Irritations provoke suddenly a very considerable increase in 

 the force of turgidity, much more considerable than is indicated by 

 the movements which take place under ordinary circumstances. 



Daily Periodicity in the Growth of Plant-stems.f — In the life- 

 phenomena of plants, there occur, under constant external conditions, 

 certain peculiar regular variations connected more or less closely with 

 certain hours of the day, and which call for investigation, as to 

 whether they are due to a direct or an indirect action of light. With 

 regard to the periodicity of the quantities of sap flowing from cut 

 stems, and the periodical movements of leaves, it was shown by 

 Baranetzky and Pfeffer that they were produced, not by the organiza- 

 tion of the plants, but by the periodical action of light, and that in 

 darkness they continued for a time as an after-action. Again, the 

 proved daily periodicity of the tension of tissues has been shown by 

 Kraus to be directly dependent on the action of light. For the 

 growth in length of stems under normal conditions of light, Sachs has 

 likewise discovered a daily periodicity, inasmuch as the growth by 

 night is always considerably greater than by day. On the other 

 hand, observations on plants which are kept continuously in darkness, 

 have not, apparently, been decisive ; for sometimes periodical varia- 

 tions appeared, and sometimes they were wholly wanting. Baranetzky 



* Arch. Ne'erl. Sci. exact, et nat., xv. (1S80) pp. 269-94. 

 t Mem. Acad. Imp. Sci. St. Petersb., xxvii. (1879)91 pp. 5 figs, and 5 charts. 

 See Np,turforscher, 1880, and Engl. Mech., xxxii. (1880) pp. 7 and 108. 



