IN VEGETABLE BIOLOGY. 597 



in the calibre of the threads : exceedingly thin at times, they are 

 occasionally so wide in parts as almost to suggest the idea of 

 rifts in the wall, but in this event it is seldom that the rift-like 

 appearance extends very far along the thread. A modification 

 of this rifting here and there occurs in the form of nodular 

 swellings fairly evenly distributed down a thread, or confined to 

 some part of its course (fig. 3). A bird's-eye view of the wall 

 (fig. 5) shows the rounded openings of the thread-embracing 

 canals ; they are larger than those of S. Nux-vomica, as will 

 immediately be seen on reference to Tangl's figure*. 



As already mentioned Tangl finds the threads of S. Nux-vomica 

 to consist only of the limiting layer of the protoplasm; this con- 

 clusion he founds upon their reaction to colouring media — 

 solutions of carmine in ammonia and in alcohol — neither of which 

 is capable of staining either the limiting layer or the threads. 

 Mr. Gardinerf was, I believe, the first to show that the threads 

 can be made to exhibit the ordinary dye-reactions of protoplasm ; 

 the best medium for this purpose he found to be a dye which 

 he calls picric Hoffman's blue J. In his just-quoted memoir 

 Gardiner enters elaborately into the nature of aniline blues 

 under the impression that Hoffman's is the only, or at all events 

 the best, dye for this purpose ; his care is, however, quite need- 

 less, for I have succeeded in staining the threads of S. Ignatia in 

 the ordinary way, first placing sections in picric acid, washing 

 and then leaving them in Judson's Oxford-blue for a few minutes, 

 and mounting in water or in strong or dilute glycerine. Ex- 

 cellent results have also been obtained with a dye prepared by 

 Gardiner's method, substituting Sands' for Hoffman's blue. 

 Gardiner's experiments tended to show that the threads do not 

 consist of the limiting layer of protoplasm alone, even if that 

 structure enters at all into their composition, Tangl's failure to 

 dye them having apparently been caused by the very faint stain 

 imparted to minute pieces of protoplasm by carmine. For per- 

 manent preparation the best mounting medium is water or 

 calcium chloride ; glycerine either pure or dilute soon causes some 

 slight change in the wall, whereby the threads become invisible ; 



* L. c. tab. v. fig. 12. t Phil. Trans, vol. 174 (1884). 



X To 100 cub. centim. of strong alcohol is added the same bulk of distilled 

 water; the solution is then saturated with picric acid, and Hoffman's blue added 

 to it until it has assumed a dark blue-green colour; it is then filtered. 



