STRUCTURE.] SCALARIFORM TISSUE. 89 



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, are also readily explained. 

 In making careful transverse and oblique sections of stems 

 of the above-mentioned plants, we can readily perceive the 

 appearances (in Plate IV. fig. 5 of Dr. Griffith, where a repre- 

 sents 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 tube gives the prismatic or angular 

 appearance to many of these tubes, so readily perceived when 

 two vessels press against each other. In some few cases a 

 large number of very small cells appear to act in compressing 

 as a single large one. When I first noticed the transitions 

 above described, I imagined they were confined to the Ferns 

 only, but I have since found them applicable to all the plants 

 above enumerated. A very common cause of the beaded 

 appearance on the margins of the tubes viewed under the 

 microscope is their longitudinal section, so that the projecting 

 extremities of the cut fibres produce the peculiar appearance 

 of beads. " These remarks are illustrated by figures in the 

 work referred to. It is to be regretted that the loose manner 

 in which the word " dots " is used should cause some obscu- 

 rity in the author's meaning. 



SECT. V. Of Laticiferous Tis&ue, or Cinenchym. 



The earlier anatomists were acquainted with the existence 

 of milk vessels in many plants, but they gave no account of 

 them sufficiently exact to distinguish them from other kinds 

 of tissue, and, accordingly, they have been usually looked 

 upon as forms of Pleurenchym, or of Trachenchym, or as 

 intercellular cavities. 



It was reserved for Prof. Schultz of Berlin to show the 

 general existence of such vessels, and their real nature, and 

 upon his and my own observations, the following account of 

 them is founded. 



Laticiferous tissue (Vital vessels, Vasa opophora) consists 

 of branched anastomosing tubes, lying in no definite position 



