FUNCT10NLESS STOMATA 475 



from the very first. In fully developed fronds of Lemna minor, however, 

 the guard-cells are,- according to the author's observations, practically 

 immovable. In the case of Limnocharis nymphoides, treatment with 

 glycerine causes the majority of the stomata to shut, but the closure is 

 often incomplete. Similarly, most of the stomata of Salvinia natans 

 even in the case of young leaves merely contract without closing 

 properly, when the internal tension of the guard cells is diminished. 

 In Impatiens parvijiora, a plant with foliage which withers very 

 readily, the stomata behave quite normally while the leaves are young. 

 The same statement applies to the stomata on the upper side of adult 

 leaves ; if the abaxial epidermis of one of the older leaves is treated 

 with glycerine, some of the stomata close completely, others merely 

 contract to a certain extent, while others again remain widely open, 

 having apparently lost all power of adjustment. In many other cases, 

 also, different stomata on one and the same leaf may lose their power of 

 movement at different times ; this difference is most probably connected 

 with the fact that all the stomata of the leaf are not of the same age. 



Stomata which never functionate from their first formation 

 onwards exemplify the process of phylogenetic loss of function. 

 According to the author's observations, the capsules of certain Mosses 

 illustrate various stages in the progressive reduction of stomata. The 

 most complete atrophy of these organs occurs in the genus Sphagnum. 

 A capsule of Sphagnum acutifolium bears more than 300 (rudimentary) 

 stomata with well-differentiated guard-cells, but not a single one of 

 these develops either a pore passage or an internal air-chamber. This 

 far-reaching reduction of the stomata is correlated with the entire 

 absence of photosynthetic tissue in the capsule of Sphagnum. 

 According to Porsch, the stomatic apparatus is always more or less 

 reduced among Phanerogamic saprophytes and parasites. It should be 

 noted, however, that even where there is no photosynthetic gas- 

 exchange, owing to the entire absence of chlorophyll, bulky and actively 

 growing aerial organs can scarcely dispense with stomata altogether, if 

 only in the interests of respiration. 



The submerged foliar and axial organs of aquatic and amphibious 

 plants are not infrequently provided with stomata, which may be 

 regarded as vestigial structures, bearing testimony to the terrestrial 

 ancestry of their possessors. According to Porsch, such stomata [which 

 are, of course, always functionless] exhibit a variety of features that 

 tend to prevent the entrance of water through them into the inter- 

 cellular spaces. 233 Thus they may have fully differentiated guard-cells, 

 but nevertheless always remain closed {CaJlitrirJir verna, Hippuris 

 vulgaris) ; in other cases, where the pore is still developed, the external 

 and internal cuticular ridges are closely appressed or interlocked (Calla 



