o4G Mr Corry, On some points in the structure and [April 30, 



Radial division now occurs in each of the four epidermal cells 

 immediately adjoining the mother-cell of the stoma (one of them 

 being the remainder of the original epidermal cell from which it 

 was cut off), but without any regular sequence : the result of this 

 is that the mother-cell is surrounded by a group or circle of four 

 cells decussating in pairs, each containing a very large and evident 

 nucleus and protoplasm which stains very deeply. This segmenta- 

 tion of complemental cells takes place in variably before the division 

 of the mother- cell in Pinus and not afterwards as Strasburger found 

 to be the case in Salisburia adiantifolia and Araucaria imbricata. 



The nucleus and protoplasmic contents of the mother-cell may 

 in the next stage be observed to have undergone division into two 

 in the longitudinal plane of the leaf, the karyolytic figure formed in 

 the change being frequently observable. This division is followed 

 immediately by the formation of a radial wall of cellulose in the 

 plane of section dividing the two parts. Thus the two guard-cells 

 are formed. When the leaf is examined in transverse section the 

 hypodermal cells, which are also elongated in the direction of the 

 length of the leaf, and which elsewhere form a layer two cells thick 

 around the periphery of the leaf, are found to be only a single cell 

 deep under each stoma-mother-cell. By this feature as well as by 

 their large size the position of the mother-cells of the stomata may 

 be easily recognised in this view at an earlier period. Two cubical 

 cells of the hypoderma appear in transverse section to underlie the 

 mother-cell of the stoma, their line of union corresponding exactly 

 to that of the divisions between the guard-cells so that the latter 

 appears to be a direct continuation of the former. The guard-cells 

 now elongate slightly in a radial direction, and since, owing to the 

 mother-cell from which they were produced being slightly angular 

 internally, the pressure which they exert in so doing is greatest 

 at that point, the underlying hypoderm cells become in accordance 

 pyriform in section and the line of union betw T een them becomes 

 rapidly reduced to a minimum. Very soon these cells separate from 

 each other laterally, leaving a small intercellular space between them 

 into which the inner and apposed ends of the guard-cells tend to 

 project. Owing to this growth downwards of the guard-cells it 

 comes about that their outer external ends are now slightly de- 

 pressed laterally from their point of connection with each other 

 below the surface of the four complemental cells of the group (two 

 of which are seen in section), and of the other epidermal cells 

 generally. 



In the next stage the lateral divergence of the two hypodermal 

 cells below the guard-cells, the downward projection of the internal 

 ends of the guard-cells into the increasing dimensions of the inter- 

 cellular space so formed, and the consequent depression of the 

 guard-cells, all become still more marked. These also form the 



