4 WATSON, Two Species of Lepidodendvon Harcouriii. 



Williamson's Terms. Terms used in this Paper.* 



( = Inner cortex. 



Inner cortex < ,„,,. 



(. = Middle cortex. 



Middle cortex ... ... = Outer cortex. 



Prosenchymatous zone ... = Periderm. 



Adenoid ... ... ,.. = Ligule. 



Description of L. Hickii; 



The material investigated consists of many sections 

 in the Cash and Wild collections of the Manchester 

 Museum, the Williamson collection, and my own. I am 

 indebted to Dr. W. E. Hoyle, the Director, for permission 

 to have sections cut from two of the Wild blocks now in 

 the Manchester Museum. 



(i) Pitk 



In a small branch, 1 35 mm. in diameter,! the 

 primary wood of which is '6 mm. in diameter, the pith is 

 composed of an irregular group of some 20 cells, which is 

 cut into by projecting tracheids. 



These cells are thin-walled and present no trace of 

 a meristematic condition. 



In a larger branch (A 171, fig. 2), which is 23^5 mm. 

 in diameter, with a wood 2 - o, mm. in diameter, the pith is 

 a more regular mass of thin-walled parenchyma 1*3 mm. 

 across. 



In this case nearly every cell towards the periphery 

 of the pith is divided up by one or more walls. 



The shape and dimensions of the original cells do 

 not, however, seem to have materially altered, although 

 we know (Seward, :oo)that in large stems, where the pith 

 was probably hollow, these cells may grow out like hypae 

 and form a felted complex. 



* These agree with those employed by Professors Bower and Weiss, 

 t Stems' are throughout measured over the leaf bases. 



