ELEMENTARY STKTJCTVRE. 



43 



Fig. 82. Fig. 83. Fig. 84. Fig. 85, Fig. 86. Fig. 87. 





s 



^ 



1^ 



5=5 



J'(>5. 82 and 83. Annular vessels. Fig. 84. Vessel 



sbowhig a conibiiialion of rings and spiral fibre. 

 . Fig. 85. Reticulated vessel. Fig. 86. Pris- 

 matic scalarifornj vessels of a Fern. — Fig. 87. 

 Cylindrical scalariforin vessels of the Vine. 



the latter they exist especially, and of a very regular character 

 in the Eqiiisetacese. 



d. Reticulated Vessels. — In these vessels the spiral convolutions 

 are more or less irregular, and connected in various ways by cross 

 or oblique fibres, so as to form a branched or netted appearance 

 {^fig. 85). These vessels are generally larger than the annular, 

 and of much more frequent occurrence. They are found in simi- 

 lar situations. 



e. Scalariform Vessels. — These are but slight modifications of 

 the reticulated vessels, and owe their peculiarity to the vails 

 being marked by transverse bars or lines, arranged over one- 

 another like the steps of a ladder, whence their name {figs. 86 

 and 87). It is frequently difficult to determine whether this ap- 

 pearance of lines or bars is caused by the secondary deposits or by 

 fibres, or whether it is not owing to the presence of spots which 

 are thinner than the surrounding parts of the wall, as is the 

 case with the pits of pitted vessels. Probably in most instances 

 at least, this is true ; while in others, it would appear to be 

 caused by the fibre, as it sometimes happens that scalariform 

 vessels may be unrolled like the true spiral vessels. Scalariform 

 vessels thus appear to form an intermediate stage between pitted 



i and spiral structures. These vessels are sometimes cylindrical 

 \ tubes like the other kinds, as in the Vine {fig. 87) and many 

 \)ther Dicotyledonous Plants, in which condition they are appa- 

 rently but slight modifications of reticulated vessels ; but in their 

 Snore perfect state, scalariform vessels assume a prismatic form, 

 as in Perns {fig. 86), of which they are then especially charac- 

 teristic. 



The annular, reticulated, and scalarifovjnxQssels constitute the 

 spurious trachecB of some authors. These vessels have com- 



