138 CONIFERALES (RECENT) 



his Juniperoid and Abietineous types. Each medullary-ray cell is 

 longer in a radial direction than the breadth of a single tracheid 

 and statements as to the number of pits on the radial wall of a 

 ray cell have reference to the area bounded laterally by the 

 vertical walls of a tracheid : this area may be designated the field 

 ('Kreuzungsfeld'; 'aire mitoyenne'). It is, however, incorrect in 

 many cases to speak of pits on the radial walls of medullary-ray 

 cells, and if pits occur they are never bordered : in the Abietineae 

 the walls are pitted, but in most other Conifers the pits seen in the 

 field belong to the tracheids in contact with the rays. But in view 

 of the general use of the expression medullary-ray pitting it would 

 be inconvenient to discontinue the cuirent terminology. There is 

 a difference of opinion as to the value of medullary-ray pitting as 

 a criterion of affinity, and it is probable that Gothan over- 

 estimates the taxonomic significance of this character. Within 

 certain limits the pitting on the walls of medullary-ray cells is 

 undoubtedly important, but a comparison of sections of the wood 

 of a collection of genera shakes one's confidence in the conclusions 

 based by some authors on the form and number of the pits in the 

 field. In the Abietineae a single large simple pit ('Eipore') 

 occupies the field in some species of Pinus but the same type 

 occurs also in Sciadopitys 1 , species of Podocarpus 2 (fig. 693, K, N), 

 Microcachrys, Dacrydium, and Phyllodadus 3 . The Araucarineae 

 are usually described as having several (2 6) oblique pits in each 

 field and as a rule no pits in the horizontal and tangential walls 

 of the ray cells, but Thomson 4 states that the bordered pits in the 

 field of Araucaria and Agathis are confined to the tracheids and 

 an examination of macerated tissue confirms the absence of pits on 

 the walls of the ray cells. A similar absence of pits characterises 

 some other Conifers. Gothan has suggested the term Cupressoid 

 pitting for Conifers in which the field in the spring- wood contains 

 bordered pits with a fairly broad pore in a more or less horizontal 

 position, a type of pitting found in some Cupressineae as also in 

 Sequoia and certain other genera. He applies the name Podo- 

 carpoid pitting to woods in which the field shows bordered pits 



1 Nakamura (83); Saporta (84) PL cxxxvm. ; Fujioka (13). 



2 Kleeberg (85). 



3 Schenk in Schimper and Schenk (90) A. p. 855. 



4 Thomson (13) p. 30. 



