206 ANATOMY OF THE GYMNOSPERMS 



deposited the lateral walls of groups of cells bear numerous rounded 

 pits, giving a sieve-plate structure. Bordered pits crowded in i row, 

 more or less rounded, not hexagonal, as broad as the narrow tracheids. 

 Pits on the tangential walls of the summer wood wanting. 

 Tangential. Rays low, only a few cells high, numerous, resinous ; the cells 

 oval, broad, thin-walled, strictly i-seriate. 

 % 



4. * * A. Woodworthi, Kn. 



" Transverse. Annual ring very obscure and not visible to the naked eye, but 

 on examination under the microscope it is found to be present and to 

 consist of only 2 or 3 slightly smaller and thicker-walled cells. The 

 wood cells are only moderately thick-walled and are quite uniform 

 in size. 



" Radial. This section shows to the best advantage the character of the wood. 

 The wood cells are shown to be long, sharp pointed, and to be provided 

 with usually 2 rows of bordered pits, although cells are common on 

 which there is but a single series. Cells on which there are 3 rows of 

 pits are much rarer. When in a single row the pits are contiguous and 

 but slightly modified in shape by pressure. When the pits are in 2 rows 

 they usually occupy the center of the cell and are contiguous and 

 slightly hexagonal ; but occasionally the 2 rows may be slightly sep- 

 arated and then may have the characters of the single rows. When 

 there are 3 rows of pits they are close together and markedly hexagonal. 

 The average diameter of the pits is about o.o 1 5 mm., and that of the 

 inner pore about 0.003 or 0.004 rnrn. The medullary rays, as seen in 

 this section, are short-celled, each cell being about as long as the width 

 of 2^ wood cells. They are without markings or pits of any kind, so 

 far as can be made out. 



" Tangential. Owing to pressure in this direction the section is somewhat 

 distorted and does not show clearly the relative abundance of the rays. 

 The number of cells entering into the composition of the rays, however, 

 shows satisfactorily. It is found that they are in a single vertical series 

 of 1-12 cells, the usual number being 3 or 4" (Knowlton). 



Material silicified. Specimen from a large, prostrate trunk 20 feet or more 



in length and over 4 feet in diameter. 

 Richmond Basin (Trias) south of Mosley Junction, Chesterfield County, 



Virginia (Knowlton). 



5. * * A. virginianum, Kn. 



" Transverse. Growth rings not obvious to the naked eye, but apparent 

 microscopically. The line of demarcation consists of only 3 or 4 rows 

 of slightly smaller and thicker-walled cells. [Growth rings obscure, 

 D.P.I'.] Tracheids prominent, with thick walls. The individual cells 

 have a diameter of 0.051 mm., the average being about 0.0375111111. 

 They are arranged in radial rows, which are most pronounced in prox- 

 imity to the medullary rays. 



" Radial. The radial walls are the only ones bearing bordered pits. The 

 number of rows varies, even on the same cell, from 1-2. When there is 

 but i row they occupy the center of the cell and are in contact. They 



