80 



FUNDAMENTALS OF CYTOLOGY 



layer being formed each day and a looser, relatively isotropic layer each 

 night. 



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Fig. 55. — Minute structure of secondary cell wall ot iiipariina. Above, delignified fiber 

 tracheid, showing radiating pattern in the remaining cellulose. Below, fiber tracheid after 

 removal of cellulose, showing radiating pattern of ligniu. {After I. W. Bailey and T. Kerr.) 



Plasmodesms. — The cell walls in plant tissues do not completel\' 

 separate the protoplasts. It appears to l)e generally true that the hitter 



