I give below a number of experimental determinations of the geo-perceptive layer in different specimens together with the micrometric measurement of the distance of the 'starch sheath' from the surface, the transverse section being made at the place where the probe entered the shoot. Eight different determinations are given, three for _Bryophyllum_ and five for _Nymphæa_. TABLE XLII.--SHOWING THE POSITION OF THE GEO-PERCEPTIVE LAYER AND OF 'STARCH SHEATH' IN DIFFERENT SPECIMENS. +-----------------------------------------------------------+ | Specimen. | Distance of | Distance of the | | | geo-perceptive layer | starch sheath | | | from surface. | from surface. | | | (Method of | (Microscopic | | | electric probe.) | measurement.) | +---------------+----------------------+--------------------+ |_Bryophyllum_: | | | | | (1) 0·6 mm. | 0·6 mm. | | | (2) 0·8 " | 0·8 " | | | (3) 0·8 " | 0·8 " | | _Nymphæa_: | | | | | (1) 0·6 " | 0·6 " | | | (2) 0·8 " | 0·8 " | | | (3) 0·8 " | 0·8 " | | | (4) 1·0 " | 1·0 " | | | (5) 1·4 " | 1·4 " | +-----------------------------------------------------------+ Thus in all specimens examined, the experimentally determined geo-perceptive layer coincided with the 'starch sheath.' The theory of statoliths thus obtains strong support from an independent line of experimental investigation. The statolithic theory has been adversely criticised because in simpler organs the geotropic action takes place in the absence of statoliths. There is no doubt that the weight of the cell contents may in certain cases be effective in geotropic stimulation; it may nevertheless be true that "at a higher level of adaptation, the geotropically sensitive members of the plant-body are furnished with special geotropic sense-organs--a striking instance of anatomico-physiological division of labour."[38] [38] Haberlandt--_Ibid_, p. 597. In the instances of _Bryophyllum_ and _Nymphæa_ given above, the geo-perceptive layer localised by means of the electric probe is definitely found to be the endodermis containing large sized starch grains. INFLUENCE OF SEASON ON GEO-ELECTRIC RESPONSE.