916 MR A. C. SEWARD AND MR A. W. HILL ON THE 



t is found to gradually pass over, in the region b of fig. 2, into regular radially disposed 

 rows of secondary tissue consisting of narrower and more elongated cells. This 

 secondary tissue composes the whole of the outermost cortex from b to the surface of 

 the stem. The appearance of the tissue is illustrated by fig. 18, PL III. ; the cells are 

 of fairly uniform size, but in some rows the elements have been tangen daily stretched ; 

 intercellular spaces are comparatively large and abundant. The same tissue is seen in 

 radial section in fig. 22, and in tangential view in fig. 20, PL III. The regular arrange- 

 ment and square ends of these elongated cells, as shown in fig. 22, is a characteristic 

 feature of the secondary cortical tissue of Lepidodendrese and Sigillarise.* The vacuo- 

 lated cell-contents seen in the tangential section, fig. 20, bear a misleading resemblance 

 to small cells ; but the cellular appearance is simply due to the manner of occurrence of 

 the cell-contents, and may be compared with the vacuolated tannin and other sub- 

 stances met with in unhealthy tissues of recent plants. The most interesting feature of 

 the phelloderm is the occurrence of seven or eight fairly regular bands of secretory cell- 

 rows, as seen at c in fig. 2, and at d, e,f, and in other parts of the phelloderm. There 

 is a row of distinct secretory groups or canals just internal to the innermost cells of the 

 phelloderm (b, fig. 2) ; each of these secretory patches contains dark indistinct traces of 

 secreted products enclosed by smaller cells lining the cavity. 



The row of secretory cells at c consists mainly of oval and circular areas, which may 

 be either empty or occupied by portions of thin-walled cells and products of secretion, 

 as shown in fig. 18, PL III. At d we have a similar row of secretory patches, but in 

 these there is rather more of the secreted material ; similarly at e and/ (fig. 2) there are 

 fairly regular bands of such tissue. In these more external rows the disorganisation of 

 the secretory elements is less advanced, and their structure is more clearly seen (PL II. 

 fig. 12). The cells forming each secretory strand are much lighter in colour than the 

 neighbouring brown cells which make up the bulk of the phelloderm. It would seem that 

 as the phelloderm was developed from a phellogen, at fairly regular intervals groups of the 

 phelloderm cells underwent further division, and constituted definite strands of secretory 

 cells. In longitudinal section a secretory strand presents the appearance shown in PL I. 

 fig. 3 ; the cells have undergone various transverse and longitudinal divisions, and some 

 of them have become disorganised, and have given rise to dark brown secretory pro- 

 ducts. A single secretory patch of cells is shown in PL IV. fig. 31 ; this is taken from 

 the region/ of the phelloderm (fig. 2), and shows a central group of cells deeply coloured 

 by the resinous or other secretion. The method of development of these secretory 

 strands appears to have been lysigenous. The superficial resemblance of the phelloderm 

 with its rows of canals to the wood of resinous Conifers is fairly striking ; a figure given 

 by Tschirch t of the resin-ducts in the wood of Copaifera Langdorjii also agrees 

 closely with our fig. 18, PL III. 



* (Jf. Williamson (72), pi. xxix. fig. 42, pi. xxxi. fig. 55 ; (72), pi. xliii. fig. 17 ; (78), pi. xxv. fig. 100. Also 

 Renault (75), pi. x. fig. 11; Renault and Grand'Eury (75), pis. iii. and v.; Brongniart (39), pi. xxvi. figs. 2 

 and 3 ; and Renault and Roche (97), pi. vi. fig. 2. 



t Tschirch (89), p. 217, fig. 216. 



