STRUCTURE.] SCALARIFORM TISSUE. 87 



by him under his division E, the pits extend into horizontal 

 fissures resembling what are called Scalariform vessels. This 

 would seem to render it probable that the last-mentioned 

 tissue belongs to Bothrenchym and not to Parenchym. 

 Scalariform tissue, which is only found in Ferns, consists of 

 angular tubes, whose sides are marked by transverse fissures, 

 or bars, which scarcely reach the angles, where all interruption 

 of continuity ceases, the angles looking under the microscope 

 like transparent lines parallel to the axis of the tube. (Fig. 

 9, and Elements of Botany, fig. 37). This is just like the 



fig.9. 



structure which Mohl represents as belonging to the Both- 

 renchym of Chilianthus arboreus. (Ann. Nat. Hist., ix, t. 8, 

 f. 2). But as Mr. Quekett says he has succeeded in unrolling 

 the scalariform vessels of Diplazium seramporense, it is as 

 well to regard them as a modification of the spiral vessel 

 until their true nature shall have been better ascertained. 

 Dr. J. W. Griffith, who figures this kind of tissue in the 

 Annals of Natural History, vol. ii, t. 4, p, 22, gives the fol- 

 lowing explanation of its origin ; it is, however, to be borne 

 in mind that he includes under the name of dotted ducts not 

 only bothrenchym, as limited in this work, but also the modi- 

 fications of spiral vessels to which the name of ducts is here 

 restricted : " When a spiral vessel has formed in a young 

 plant, the rapid growth of the stem induces considerable 

 pressure of the surrounding parts ; the consequence is, that 

 the convexity or parts of the surrounding vessels or cells 

 opposite to the spiral vessel are pressed firmly against it, whilst 



