172 



THE ANATOMY OF WOODY PLANTS 



this involves no erroneous hypothesis of their relation to the pith. 

 It is therefore necessary to distinguish carefully between wood rays 

 and gaps or discontinuities in the woody cylinder originating as a 

 result of conditions described above. It seems quite evident that 

 the failure to realize this distinction invalidates investigations on 

 the woody cylinder involving the confusion of thought elucidated 



by the items in 



t e accompanying 

 figure. 



The last para- 

 graph will have con- 

 vinced the reader 

 that radial bands of 

 parenchyma, formed 

 as a result of cam- 

 bial activity, can- 

 not accurately be 

 described as medul- 

 lary rays. We are 

 now in a position to 

 consider the situa- 

 tion presented by 

 the stem of peren- 

 nial seed plants of 

 gymnospermous af- 

 finities. Fig. 123 reproduces part of a transverse section of a stem 

 of the white spruce, Picea canadensis. The woody cylinder is 

 characterized by numerous radial bands of parenchyma, appar- 

 ently in every instance taking their origin from the medulla or 

 pith. Further, there are present broad outwardly directed bays 

 from the medullary region which represent the gaps correspond- 

 ing to outgoing leaves (for in the gymnosperms, in contrast to 

 the lycopods and their allies, the leaves are related to foliar gaps). 

 A superficial examination of the figure would justify the applica- 

 tion of the term medullary ray both to the narrow radial bands of 

 parenchyma and to the broader bays extending from the pith. 

 The considerations advanced in the last paragraph make it clear, 



FIG. 123. Stem of Picea, showing apparent relation 

 of wood rays to pith. 



