[Ectodesmata and the peristomatal transpiration]

The total transpiration is the sum of stomatal and epidermal transpiration. The latter consists of 1. the cuticular transpiration, or exhalation of water vapour through the cuticle of epidermis cells, and 2. the recently defined peristomatal transpiration (SEYBOLD, 1961/62), which means the exhalation of water vapour through the guard-cells and their accessory cells. MAERCKER (1964, 1965 a, b) has demonstrated this peristomatal transpiration by microautoradiography using tritiated water. In the investigations described here the characteristic patterns of silver deposits in the radioautographs which are to be found over the guard-cells are compared with the distribution of ectodesmata in the outer epidermal walls of leaves of the same species which were used in the transpiration studies. It can be shown that the sites of highest blackening of the stripping film, i. e. the places of water vapour exhalation, correspond to the sites where ectodesmata occur in large numbers. In the case of Zantedeschia aethiopica clear pointlike accumulations of silver grains which have a distribution pattern similar to or identical with that of ectodesmata are to be seen in the stripping film. This observation strongly suggests that ectodesmata behave as portals of exit of water vapour in the guard-cells and their accessory cells. These findings coincide with earlier reports on the connection between cuticular excretion of substances and the distribution of ectodesmata. The possible function of ectodesmata in cuticular and peristomatal transpiration is discussed.