Stoinata. '69 



cuticle of a leaf, wo find both the closed and open stomata very 

 numerous. This may de])end on the time of the day or the state 

 of the atmosphere as regards moisture, or vary according to the 

 nature of the plant. When they are flaccid they are closed, that 

 is to say the guard cases reuiain closely applied, and the orifice is 

 covered over; but under ordinary conditions of the atmosphere 

 they are open ; when it is either very dry or very moist they are 

 generally closed. The whole working of the system reuiains to be 

 accurately examined. It is also to be desired that in time, as Mr. 

 Brown first suggested, we may be able to distinguish natural orders 

 and even genera of plants by the shape and position of their 

 stomata, as well as by their size with respect to the meshes of the 

 cuticle. As it is we know that of the two great classes of flowering 

 plants the dicotyledonous and the monocotyledonous, the latter is 

 distinguished by the greater size and number of its stomata, and 

 this being so, why should not the smaller divisions of genera and 

 their natural sections be distinguished by the shape and particular 

 qualities of theirs also ? Especially as in examining any number 

 of plants of different genera, we notice no two with stomata of 

 exactly the same shape. 



In the same way the position and general arrangement might be 

 marked, as we know that the large order of graminese and some 

 others of endogenous plants have their stomata at regular distances 

 from one another, and disposed in rows parallel with the bundles 

 of tissue of which the leaf is composed ; and also in exogenous 

 plants ihe firs are marked by the same arrangement. In Begonia 

 and some tropical plants of the order crassulaceae they are arranged 

 in rosettes ; still in far the greater number of plants they appear to 

 be scattered at irregular distances over the whole surface of the 

 cuticle. 



Mr. Brown has himself followed up his theory founded on these 

 distinctions in one order, the Proteacea;, of South Africa, in nearly 

 all the plants of which they are found on both sides of the leaf in 

 nearly equal abundance. 



As a rule they may be said to exist on all cuticle exposed to the 

 air, but turned away from the direct rays of the sun ; from very 

 succulent plants however, they are said to be altogether absent. 



They are not found on plants that grow in the darkness, nor 

 uj)on roots, nor on parasites that are destitute of colour; neither 

 are they to be seen on submersed plants, or the submersed parts 

 of water plants, so that on floating leaves of the water lily they are 

 found contrary to the rule on the upper side only : and on plants 

 turning the margin of their leaves towards the earth and the sky the 

 two sides are equnlUj covered tvith stoinata, and have the same 

 appearance, and Mr. Brown has remarked that it is to the micro- 



