236 MR. S. LE M. MOOBE'S STUDIES 



callus and paracallus, the callus of eosin sections having given 

 up its eosin and taken the blue of the other sections, while 

 the paracallus had monopolized the eosin and had become deeply 

 dyed with it. Of course it is usually fairly easy for the practised 

 eye to distinguish between callus and paracallus; and if there 

 should be any doubt on the point, it can soon be dissipated 

 by the use of picric blue, with which callus stains a Cambridge, and 

 paracallus (if at all) an Oxford-blue. I experienced most difficulty 

 in dealing with theDog-Eose, masses which in this case I thought 

 to be callus often proving to be paracallus, and vice versa. 



We thus see how, a propos of the methods whereby the 

 sieves are closed up, we are able to write down the following 



series : 



In Ballia we have paracallus alone. 



In Rosa caninct, Ampelopsis hederacea and Veitchi, the Fig, 

 and Macrocystis pyrifera we have callus and paracallus. 

 In the Ash and the Elm we have callus alone. 



Is True Callus Soluble in any Organic Fluid? 



We can frequently get information about the nature of a sub- 

 stance by studying its solubilities, and this consideration led me 

 to try the eifect of diastatic ferments npon callus. The method 

 consisted in introducing thin radial longitudinal sections into 

 vessels containing the ferment, these being kept for some time 

 at a temperature higher than that of the air, and generally at, or 

 a little below, that of the human body. I hare already mentioned 

 the want of success in working with a pancreatic fluid, and as 

 this, besides trypsin and steapsin, contained diastase as well, we 

 are forced to conclude that callus is untouched by a diastatic 

 ferment. This conclusion was borne out on treatment of Fig, 

 Ash, and Elm sections with saliva for 60 hours, and for 140 hours 

 with Kepler's malt extract, which contains a powerful diastatic 

 ferment. 



I then turned to gum-arabic with the idea that, as callus is 

 generally supposed to be of mucilaginous nature, a solvent for it 

 might possibly be found in the gum. In this surmise I was not 

 mistaken ; and I have several times successfully repeated my 

 observations, which were made especially upon the Fig and the Ash. 

 Eeference to PI. XXV. fig. 4 will brin" to the eye what happens 

 when a section of Ash-bast is placed in a solution of gum-arabic ; 

 in this ease the action lasted for 49 hours at or near the tern- 



