MacMillan : OnisERVATioNS ox Nekeocvstis 291 



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before the time of their differentiation, nor are cryptostomataabun- 

 dant tp\Y£ird tl^e^^tip of the leaf. 



Splitting of the Lamina . — From a series of sections taken 

 through young laminae of a plant m which the first cleft is begin- 



ning to appear I have been able to determine the origin and oc- 



casion of the cleft. In Ncrcocystis the cleft does not appear to be 

 of the nature of a wound as said by Professor Setchell of the similar 

 phenomenon in Saccorliiza dcrjiiatodca^ but it seems to take place 

 in this way : A single row of cortical cells immediately below the 

 epidermis deliquesces or collapses and the epidermis furrows along 

 the depression. The deliquescence is propagated to adjacent cells 

 ri":ht and left of the furrow^ and continues down to the middle 

 lamella. This furrowing may take place along one surface of the 

 leaf or along both surfaces until the epidermal cells come to he 

 against the middle lamella. The latter then breaks down and the 

 two epidermises at the bases of the furrows are contiguous. The 



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5plit takes place along the base of the furrow and leaves the two 

 Jialves of the lamina with apparently normal unwounded edges. 

 In some cases the cortex cells come down together over the edge 

 of the deliquescing central lamina so that it is extremely difficult 

 to distinguish between the original edge of the lamina and the edge 

 of the cleft. The cpide^rmis suffers no disintegration during the 



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'process. The actual cleavage of the lamina may be due, as Pro- 

 fessor Setchell suggests for SaccorJiiza^ purely to the impact of the 

 waves upon the weakened structure, but it may also be due to a 

 definite separation of the epidermal cells from each other by a 

 chemical change in their walls. The furrow of the epidermis seems 

 - to deepen, destroying the inner cells of the lamina as it progresses. 

 The split takes place first in the more complex basal portion of the 



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leaf and is perpetuated to the tip. I have not been able to de- 



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termine whether the cleft is propagated in this manner clear to the 

 simpler primitive-tip end of the leaf, or w^hether it becomes a 



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mechanical cleft of the nature of a w^ound when it reaches the distal 

 end of the lamina. 



No evidence has been secured to indicate that there is any 



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renovation of the lamina in Ncrcocystis such as is well known to 

 take place in some of the Laminariaceae. 

 ' Structure of the Cryptostouiata. — The organs of the young stipe 



