98 Dr. Griffith on the Formation of 



less ; thus the fibre withhi the compressed spiral is bent into 

 as many sides as there are surrounding and pressing vesicles or 

 vessels. This is illustrated in fig. 14 ; accordingly, if the spiral 

 fibre be examined at this period it will be found bent as above 

 mentioned, and the natural curve of the fibre straightened. 

 Opposite the intercellular or intervascular spaces, i. e. at the 

 bendings of the fibres, the latter become firmly adherent to 

 the membrane, thickened and united to the fibres above and 

 below. These thickened portions form the line of space run- 

 ning between the rows of dots. The dots themselves are 

 formed by the spaces left between the portions of the fibres 

 opposite the convexity of the surrounding cells and vessels. 

 Thus, when we examine the tubes at this stage, we find the 

 membrane and fibre united so firmly that they are with great 

 difficulty separated. The vegetable substance which fills up 

 the intercellular spaces often also becomes firmly adherent to 

 the membrane and fibre, so that when we dissect out these 

 tubes from the surrounding parts we often find the remains 

 of adherent portions which existed opposite the intercellular 

 spaces ; therefore the number and arrangement of the dots 

 must depend entirely upon the surrounding vessels and cells. 

 When the compressing and compressed tubes are equal in 

 size, the dots extend nearly across the face or opposed side 

 of the tube ; and when several small tubes and vessels com- 

 press a spiral so as to convert it into a dotted tube, the dots 

 will be small and numerous. The observation of Schleiden, 

 that, " in consequence of the deposition of formative substance, 

 the pore appears the rounder the more the cell is developed," 

 is, 1 think, incorrect — I believe the reverse to be correct. The 

 examination of the young and old stems of anj^ plant con- 

 taining these vessels will prove this. If the fibre be separated 

 from the surrounding parts in the early stages, it will be found 

 bent and thickened at the bendings ; and oftentimes we can 

 find portions of membrane &c. adhering as above mentioned. 

 These vessels are generally observed in plants whose growth is 

 rapid, so that in the older stems we cannot expect to find the 

 arrangement persistent ; but in a large number of plants it 

 can readily be perceived, especially where the formation has 

 not been completed. We can now readily account for the 

 impression of a small tube sometimes observed as imprinted 

 on a larger one ; the black lines running between the dots 

 and separating their rows is also readily explained. In making 

 careful transverse and obJique sections of stems of the above- 

 mentioned plants, we can readily perceive the appearances 

 sketched in PI. IV. fig. 5, where a represents the rows of dots 

 corresponding to the projecting portion of the cell opposed to 

 the forming tube. The bent appearance of the fibre within the 



