IN VEGETABLE BIOLOGT. 235 



the winter, blocked up with masses of paracallus. Examples of 

 this are shown, PJ. XXV. figs. 3 a, b, c, and d. Of these, a repre- 

 sents a small mass ; b one upon a side-wall, seen in profile ; c a para- 

 callus-cap, recalling a 2?aZft#-stopper, hanging by paracallus-(?) 

 threads to the sieve-plate from which it has been disturbed by 

 sectioning; at d is drawn a large mass blocking two sieves from 

 which sectioning has partly dislodged it. This paracallus gives 

 good proteid reactions; and in some cases efforts to peptonize 

 it met with success, though failure was sometimes experienced 

 even after lengthy action of a gastric or pancreatic fluid. 



Some General Remarks. 



Experiments were also made with the Elm, with Ampelopsis 

 Jiederacea and VeitcJii. Of these, the former resembles the Ash ; 

 for I could find no paracallus upon its sieve-plates ; while the 

 two latter are more like the Dog-Bose inasmuch as paracallus is 

 frequently seen in them. The callus of the rhizome of Arundo 

 Phragmites is also true callus ; though unfortunately, from its 

 paucity upon the sieves of my material, I have not been able to 

 make a thorough examination of it. 



It might perhaps be objected that the paracallus is merely 

 that somew hat denser condition of the slime met with at one or 

 both ends of the sieve-tubes — usually at one end — and called by 

 German writers " Schleimkopf." It undoubtedly is formed from 

 the Schleimkopf, towards which it seems to bear the same 

 relation that the Schleimkopf itself does to the slime. This is well 

 seen in large cells of JBallia, in which we often find aggregation 

 of the contents at one or at either end of the cell, which is capped 

 by the paracallus-stopper. Apart from its function of obstructing 

 the sieves, paracallus differs from Schleimkopf in its so frequent 

 refusal to take up carmine and aniline-blue. Its chief differences 

 from true callus have already been explained, though in this 

 connexion one matter of interest must now be mentioned. Both 

 callus and paracallus stain well with watery eosin ; but whe 

 the stain taken by the former is not permanent, that imparted to 

 the latter is so. I recently came across a beautiful instance ot* 

 this. A few years ago I mounted, under one coverslip, some 

 large sections of Vegetable-Marrow bast showing well-developed 

 callus; these had been stained some in watery eosin, others in 

 picric Sands's blue, and happening recently to examine the slide, 

 I found that an interchange of stain had taken place betweeu 



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