1883.] Significance of Water Glands and Nectaries. 39 



My results in every way confirmed Sach's statement, that the 

 exudation in typical water-glands is dependent upon root-pressure, 

 and does not take place from the leaves of parts of plants which 

 have been cut off, under water, and placed under a bell-jar standing 

 over water. Although most careful and most numerous experiments 

 were made, I was unable to observe any exudation of water from such 

 cut parts of plants. When however, as in many of the Crassidaceae, 

 adventitious roots into the water were subsequently formed, there 

 was at once a normal exudation. 



Moll, on the other hand, maintains that in certain instances, 

 e.g. species of Impatiens and Fuchsia, the exudation of water from 

 the teeth does take place independently of root-pressure. In ex- 

 perimenting upon this question my results appear to show that this 

 is not the case. With regard to Impatiens I find that the leaf- 

 tooth is, as in many other instances, e.g. Callicoma sp. and Fra- 

 graria vesca, a composite structure; for the cells of the summit 

 of the tooth are modified so as to form a nectary, while the 

 true water-gland and water-pores are situated at its base 1 . In 

 young leaves there does occur a secretion of drops of nectar, but 

 the water-gland, as such, is inactive in the absence of root- 

 pressure. 



In the case of Fuchsia globosa some very interesting results 

 have been obtained, for I find that if a shoot of this plant be cut off 

 under water and placed with the usual precautions under a bell-jar, 

 the younger leaves become bedewed with moisture, and that in 

 some cases drops are situated at the apices of many of the leaf- 

 teeth. The water, however, does not come from the glands but 

 from the numerous hairs with which the surface of the leaf is 

 freely clothed. That this is actually the case I have proved from 

 repeated experiments which were again and again varied, the 

 temperature being quite constant and every possible precaution 

 being taken. The water so exuded frequently collects on the 

 teeth, being derived from the hairs in their immediate vicinity, and 

 gives the appearance of an exudation from the water-gland. I found 

 in addition that the hairs of other young leaves will also exude 

 w r ater in the same way : the phenomenon being of course simply 

 the expression of that very great activity, which is especialry the 

 attribute of epidermal tissue ; in virtue of which the water is sucked 

 up on one side and exuded on the other, and I have but little 

 doubt that in certain instances this water may contain salts in 

 solution. This will at once account for the presence of incrusta- 



1 It seems probable that the cellular bodies described by Francis Darwin on 

 the apices of the leaflets of Acacia splicerocephala are of the same morphological 

 value as these structures. See Linnsan Society Journal 1877. See also Eeinke 

 (I. c). 



