590 Physiologie. 



Wölk, P. C. van der, Physiological researches concerning 

 the latex problem. (Publ. Physiol. veg. Nimegue. II. p. 1 — 33. 1914.) 



By studying the outflow of latex under different conditions and 

 comparing the wateriness of the milksap, the writer believes to 

 have proved, that latex formation is a tunction of living cells i.e. 

 of secretion and may occur arbitrarih^ in an}^ separate part of the 

 plant. The formation of latex is also induced by the wound Stimulus, 

 Investigation proved that the latex is not employed as a reserve- 

 material. 



It seems that the milksap cells exert a strong glandulär action 

 even in the normal intact life of the tree and the author supposes 

 that in normal conditions the latex must be regarded as the con- 

 structive material for cell-walls, Th. Weevers. 



Wölk, P. C. van der, Researches con taining geocarpy. 

 (Publ. physiol. veg. Nimegue. II. p. 34—54. 1914.) 



The writer regards the subterranean fruit of Arachis hypogaea 

 as no true fruit but as a rhizom within which the true pod is en- 

 closed. The ovary is enveloped by a receptacle, which becomes 

 elongated and as a stalk shaped organ penetrates into the ground. 

 The top of the stalk then curves horizontally, begins to swell and 

 forms the fruit in a horizontal direction. 



ßy trying this fructification under different artificial conditions, 

 for instance occluded from light, wrapped in filterpaper wetted with 

 rain water etc. the results were always negative; only with wet 

 mould or extracts of rieh soll the effect was successfull. Herefrom 

 the author concludes, that the fructification is a function of the 

 action of chemical materials, which are found in the soil and that 

 this action must not be considered as a Stimulus but as a nourishing 

 process. 



In the case of Voatidseia suhterrmiea the flower is formed Under- 

 ground, tecundation takes place cleistogamically ; after fecundation 

 the upright flower-pedunculus bends itself positive geotropically 

 downwards and afterwards fruitsetting takes place. When the fruit 

 has attained a diameter of 1 mM the flowerpeduncle curves in a j 

 parallelotropic sense so that it comes to lie horizontall5^ The fruit " 

 is here a true pod. 



Various experiments concerning fruit formation above ground 

 were made. Treating with concentrated soil extract gave the best 

 results, so that it is concluded that the fruits take themselves their 

 inorganic nutriment from the ground. Th. Weevers. 



Wölk, P. C. van der, Researches in the Ph3^siology of 

 T üb er for min g. (Publ. Physiol. veg. Nimegue. II. p. 55— 66. 1914.) 



The tuberforming of Iponioea Batatas was studied especially 

 the forming of the by tubers These are formed on the roots, which 

 first run in a more or less horizontal direction at the spot where 

 these roots suddenly turn up perpendicular downwards. This for- 

 ming occurs at a definite distance under the surface in consequence 

 of the planting of the sweet potatoes in ridges. 



The roots, neither in the laboratory nor in the open field do 

 appear to be sensitive to light or warmth, but the curving occurs 

 in the boundary of a cork dry and a more or less damp region. From 



