28o 



'.ECTURE XVI. 



of water dropped in one night from the leaves of Colocasia antiquorum. According 

 to a statement by Müsset, the drops of water forced out may even be projected 

 to a distance of several centimetres. Whether the excretion of drops has any 

 favourable significance for the plant, and what, is still unknown ; though, con- 

 sidering the generality of the phenomenon, it seems scarcely possible to deny 

 that it must be of advantage in the economy of the plant. Moreover this water 

 is, of course, not pure water : on the contrary, it contains traces of the salts taken 

 up by the plant, and occasionally also organic substances as well. On rapid 

 evaporation of the excreted drops, these matters may remain behind as solid 

 masses; and in this way are explained the calcareous scales on the margins of 



the leaves of many Saxifrages. 

 This shows, however, that spe- 

 cial relations of organisation 

 co-operate here, since they do 

 not occur in the majority of 

 other plants \ 



I have already repeatedly 

 mentioned in preceding lec- 

 tures that the relations of or- 

 ganisation and vital pheno- 

 mena of highly organised plants 

 consisting of differentiated 

 masses of tissue, are again 

 usually to be met with also in 

 such very simply organised 

 plants as in the CccloblasfcB, 

 which never undergo cell-di- 

 vision in the course of their 

 growth. So also the excretion 

 of drops is observed among the 

 Fungi, on the sporangia of 

 species of Mucor. These plants 

 consist, as was shown at p. 5, of 

 copiously branched tubes, their 

 root-portion or mycelium (Fig. 

 2 1 7 ni) being extended in the nourishing substratum, while thicker tubes grow per- 

 pendicularly from these into the air, and form the sporangia at their ends. On these 

 sporangia, when they have attained a height of several centimetres, numerous small 

 drops of water now appear, which are evidently being forced out through the closed 

 membrane; the pressure necessary for this, however, is evidently afforded by the 

 endosmotic absorption of the roots in the substratum, and we have here at once 

 •the simplest conceivable case of root-pressure, since the entire plant consists of a 

 single tube, never divided off by transverse walls. Thus it is the parts of the tube 



-Phycomyces nitens. 



1 With respect to the calcareous scales on the leaves referred to, cf. De Bary's ' Vcrgl. Anat. 

 der Vegetations-organe' (1877, p, 57). 



