354 PEOF. H. M. WARD AND MISS E. DALE ON CRATEROSTIGMA PUMILUM. 



be that the colour is merely incidental, and that it is the granules themselves which are 

 of use to the plant. 



In discussing the uses of carotin to the plants in which he found it, Zopf suggests three 



possible functions for the colour : — 



(1) That it is a protection against light; 



(2) That it protects the plant against the attacks of plant-eating animals ; 



(3) That it is a reserve material. 



The first hypothesis is untenable in the case of our plant, because the colour occurs in 

 those parts of the plants which are not exposed to the light. 



The second suggestion was abandoned by Zopf because, in the case of carrots, carotin 

 is no protection from the attacks of snails and other animals. 



The third suggestion seems to us to be extremely improbable, especially as the colouring- 

 matter is produced in such large quantities in the intercellular spaces in perfectly active 

 organs. And, as we find no evidence of resorption, it may be taken to be an excretion. 



It may be that some of the peculiarities of the colouring-matter in our plant are 

 due to its environment*. In this connexion Zopf's w^ork on Trentepohlia lolithus^ 

 Wallr., an alga growing on bare rocks, is interesting and suggestive. In this plant, 

 which is alternately dried up by sun and wind and brought into a resting condition, and 

 supplied with w^ater by rain and dew and so enabled to grow, the reserve materials take 

 the form of oil-drops and of included crystals of carotin, i. e. of bodies wdiich are insoluble 

 in water. 



It may be that a reserve material which is insoluble in water would be more stable 

 and less liable to be influenced by metabolic changes dependent upon fluctuations in the 

 amount of water present in the plant, especially if, as is the case in Crate rostigma, it is 

 placed outside the cells. 



But it is difficult on any hypothesis but that of excretion to account for the position of 

 the granules outside the cells. 



EXPLANATION OF THE PLATES. 



Plate XXXIV. 



Fig. 1. Whole plant, about natural size, showing leaf-rosette and red roots springing from the snort 

 root-stock (also red), one fully-expanded flower and two from which the corolla has tallen. 



Fig. 2. A stolon with three buds, somewhat enlarged. 



Fig. 3. Cross section of a bud, slightly magnified, showing sub-opposite leaves. 



Fig. 4. Flower-bud viewed (a) from the side, [h) from below — anterior view, (c) from above— posterior 

 view. 



Fig. 5. Corolla seen from [a] the side, {b) above, and (c) below. , 



We believe that our plant comes from a rocky region, where it would be exposed to periodic droughts. 



