24 



Miss E. R. Saunders. On a Discontinuous 



Histological Note. 



A microscopical examination of the leaves revealed the presence of 

 a histological feature of some interest. The general arrangement of 

 the tissues follows the normal dorsiventral type ; it is the mesophyll, 

 however, which claims especial attention, and exhibits a structural 

 peculiarity which consists in the thickening and lignification of the 

 cell walls in such a way as to form a latticed network. The meso- 

 phyll cells of the cylindrical leaves of some species of Sansevieria 

 exhibit a somewhat similar appearance as has been previously recorded 

 by De Bary,* and figured by Henfrey.f These bands of thickening 

 give the characteristic lignin reaction with Schulze's solution and 

 with phloroglucin. In all respects, save for this modification of the 

 walls, these cells resemble the rest of the mesophyll, and judging 

 from the amount of chlorophyll contained in them, their capacity for 

 amylogenesis is not less than that of the unaltered cells. The number 

 and distribution of these cells varies considerably in different cases, 

 but so far as I have been able to ascertain, their occurrence is not 

 correlated with any other structural feature. In order to determine 

 their presence or absence in any given case, the leaves to be examined 

 were allowed to rot in water until the epidermal layer could be easily 

 peeled off with forceps from the under surface ; they were then 

 mounted whole, with the under surface uppermost. When sufficient 

 transparency could only be attained by decolorisation, the leaves were 

 placed in alcohol, and afterwards boiled for a few minutes in water or 

 in dilute HC1, to facilitate the removal of the epidermis. The method 

 of examination by sections was found to give unreliable results, since 

 the distribution of the cells is so erratic that their non-occurrence in a 

 number of sections affords no certain criterion of their absence from 

 the whole leaf. They may occur singly and remote from one 

 another, or in groups in the meshes of the fibro-vascular network ; or 

 continuous layers of the spongy mesophyll or of the palisade cells may 

 undergo this modification ; in one case they may cover an un- 

 interrupted area almost as large as the leaf surface, in another they 

 may perhaps be confined, to one side of the midrib, and be wholly 

 wanting on the other, in fact, their distribution would appear to be 

 entirely haphazard. In some cases they are present in the cotyle- 

 dons, but more often they are absent from these organs, though they 

 may be present in the later-formed leaves of the same plants ; their 

 presence in one leaf does not necessarily imply their occurrence in 

 other leaves of the same individual. To take a single instance — nine 

 leaves belonging to a very hairy plant were examined ; in five of these 

 the cells were abundant everywhere ; in two a few were present ; and 



# ' Comparative Anatomy of Phanerogams and Ferns,' p. 118. 

 f ' Elementary Course of Botany,' p. 483 (2nd edition). 



