iQii] Francis Ernest Lloyd ii 



tannin cells, and the Spilling of their contents. The application o£ 

 a tannin reagent then causes a general stain^ which obscures the 

 structures of the cells it is sought to study, while the addition of 

 water or glycerol causes disturbances which destroy their structure. 

 There is only one way to see the tannin-cell without damage or dis- 

 tortion and that is to mount a small piece of tissue, cover with a 

 light thin cover, and to examine the preparation where the air has 

 been excluded by the fluids of the tissue itself. The addition of 

 various agents will then enable the observer to test the nature of the 

 structures seen. I particularly mention this, as the usual directions 

 in text-books indicate the use of reagents and mounting media 

 without reference to their physical effects upon the cell contents. 

 It scarcely need be said that, for one study ing such an object for 

 the first time, it is necessary to identify the tannin cells in order 

 to become sufficiently familiär with them to recognize them un- 

 stained. 



In form, the cells in question vary from long, slender cylin- 

 drical to isodiametric (figs. i, 2, 15), the general size and more 

 prevalent form being more or less characteristic of the species 

 (Howard, 1906) but also determined by the position of the cells 

 within the fruit. The articulation with adjacent parenchyma cells 

 is by means of facets and shallow pores; that with neighboring 

 tannin cells by means of short cylindrical projections forming 

 bridges (Howard, 1906). In an isolated tannin cell, these pro- 

 jections offer points of vantage for the Observation of the behavior 

 of the protoplasm and its inclusions under internal pressure to be 

 described beyond. The wall reacts blue to iodine, indicating its 

 pectocellulosic nature. During the early period of ripening, indi- 

 cated by very slight softness in the fruit, the middle lamella is 

 digested, and the tannin and pulp cells (as I shall hereafter call 

 the non-tanniferous cells) are then easily separated, and can be 

 more carefully studied. It is during this period that critical study 

 of individual cells is possible for the first time in the course of ripen- 

 ing. Comparison with these cells in the still hard fruit shows that 

 they may be had in the same physiological condition just after, as 

 well as before, the initial softening of the middle lamella. In 



* Strasburger : Practical Botany, 6th ed., p. 429. 



