1907] 



BARNES &- LAND— ORIGIN OF AIR CHAMBERS 



207 



i 



I 



a posterior cell. Each is then divided, in the plane ^ **, into a 

 superficial and an internal cell by a periclinal division, and at the 

 intersection of these last walls with the preced- 

 ing anticlinal one^ ^2, the spHt usually occurs. 

 This is promptly followed by divisions, ^ ^, 

 to form the cells of pore margin and roof. 

 I^ fig' 5 the four nuclei mark the place of the 

 split; for were the division in progress com- 

 pleted, the cleft would appear at the corner 

 common to these four cells. 



There is also more or less variation in the 

 course of development. Sometimes the nascent 



chamber breaks out to 



the surface and re- 



mains wide open for Fig. y.—Marchanila 



a time (fig. 7, ^ ) ; poly mo rpha: a, ^plcBl cell; 



/ 1 2j 7, air chambers; at I 



sometimes (and more ^ _^ -jr. 



^ the next one is due after 



commonly) divisions division of outer cells. 

 Fig. 8. — Marchantia ^nsue SO promptly in 

 polymorpha: j, 2, air cham- the cclls above the primary cleft that the 



!5!'!L/J.^''IL^''^^ ^^' turgor of the newly formed cells keeps the 



passage closed from the beginning {figs. 



sion of roof cells. 



6, 

 6. 



3. 



3. 



s, 



1,2 



7; 



3. 



3 



). These quickly divide {figs, 

 g) and by repeated divisions give 



of the well-known form. 



{fig 



fig 



Fig. 9 



Marchantia 



plate 12, of Leitgeb's Untersuchung 



the earlier figures of his paper on the stomata 



of ^Marchantia (/. 6., footnote 3), shows 



clearly enough that he saw essentially similar 



stages, though probably not such early ones 



as we indicate. It was chiefly in the interpre- sion of the "mother ccir' of 



tation of his obsen^ations that he went ^^ ^'^ chamber; the num- 



astray. 



V 



polymorph a , Diagra 



the course of normal 



of 



In Lunularia the process is similar in all 



bars show the sequence 

 of walls. 



Marchantia, though the ma 



