L. Wills — Plant Cuticles, Coal-measures. 389 



the tissue and the presence of spore-tetrads embedded in the thallus, 

 points to the possibility of its being a primitive type of Bryophyte. 

 Should further study support this view, these specimens -will be 

 of great interest as being the first Bryophytes recorded from the 

 Palaeozoic rocks. 



4. Conclusions. 



1. Morphological. — The chief interest in a study of the structure 

 of a leaf cuticle centres round the stomata. In the specimens 

 described above one type of stoma is common to all the species. 

 The type is simple. A girdle of subsidiary cells surrounds the 

 stomatal cavity, forming a ring of thickening where they abut on to it. 

 The two guard-cells are slightly sunk in the stomatal cavity. The 

 prevalence of this simple uniform type of stoma is of interest, since 

 the cuticles examined by Professor Zeiller and Dr. Huth respectively 

 showed distinct differences of stomatal structures, and in the case of 

 Alethopteris the structure observed was interpreted differently by 

 the two observers. Professor Zeiller ^ concluded that the guard-cells, 

 which were missing in his specimen, were origiu;illy present but had 

 not been preserved. Lr. Huth,- however, maintains that in all 

 probability the guard-cells were never present, and that stomata were 

 of an aquatic type similar to those in Mariopteris vniricata. The 

 description of the stomata of AletJwpteris given above entirely bears 

 out Zeiller's contention, but it is hoped that a further study will throw 

 more light on this structural point. 



2. Ecological. — The discovery of cuticular remains in the Coal- 

 measures is of importance ecologically, since the epidermal features 

 of a plant, especially the arrangement, structure, and number of the 

 stomata, are intimately related to climate and habitat. Yet results 

 based on the cursory examination of a few species can be of little 

 value, and I do not propose to do more than make a few tentative 

 suggestions. Dr. Huth has already suggested that the aquatic type 

 of stoma found in Mariopteris muricata indicates an extremely humid 

 atmosphere. The different types of cuticular structure found in 

 Neuropteris heterophylla and Cyclopteris would seem to lend support 

 to this view, for such authorities as Warming ^ and Haberlaudt * cite 

 water-pores, glandular patches, and liairs on the epidermis as 

 characteristics of plants living under humid conditions. If we 

 assume that these structures functioned as hydathodes it is probable 

 that the hairs and glandular patches occurred on the lower surface of 

 the leaf and the water-stomata on the upper. If this be so, the 

 stomata are more numerous on the ujiper surface, a feature which is 

 consistent with the view that the plants were hygrophytic. Yet the 

 number of stomata is less than might have been expected under such 

 circumstances. 



3. Phjlogenetic. — It is possible that the structure of the stomata 

 may eventually prove of use in tracing the ])hylogeny of modern 

 forms. Suggestive in this respect is the similarity between the 



^ R. Zeiller, op. cit. 



2 W. Huth, op. cit. 



^ E. Warming, Ecology of Plants, English trans., 1909, p. 101. 



* G. Haberlaudt, op. cit., pp. 445, 451. 



