SPECIAL METHODS. 245 



erally necessary to leave the objects from 5 to 24 hours 

 in the solutions. 



A more rapid reaction is obtained with a more concen- 

 trated solution containing I gram AgNO 8 and .3 gram NH V 

 to a liter of water. This can be used, however, only with 

 resistant objects and with such as contain neither sugar nor 

 tannin (cf. Bokorny VI, 195). 



22. Protoplasmic Connections. 



449. Proof has been furnished by the investigations of 

 Tangl, Gardiner, Russow, and others that, besides the ele- 

 ments of the sieve-tubes, the protoplasts of the separate 

 cells of various other tissue-systems are in direct connection 

 with each other through perforations of their cell-walls.. 

 Kienitz-Gerloff (I, 22) has recently concluded from his re- 

 searches that all the living elements of the entire body of 

 the higher plants are united by protoplasmic threads. The 

 threads which accomplish this union, the so-called proto- 

 plasmic connections, are, however, in most cases so fine that 

 nothing can be seen of them within the living cell ; and 

 rather complicated preparation-methods are necessary to- 

 their recognition. 



450- If one has to do with relatively thick protoplasmic 

 connections, like those of many sieve-tubes, they may be 

 made visible, in many cases, simply by treatment with 

 chloroi'odide of zinc or with iodine and sulphuric acid. 

 Gardiner (II, 55, note 4) recommended for this purpose a 

 solution of Hofmann's violet in concentrated sulphuric acid. 

 This solution has a brownish color and does not stain strorigly 

 sections placed in it. But if the acid is washed out with a 

 large quantity of water, after acting for about half a minute,, 

 the sections take at first a green, then a bluish, and finally a 

 violet color, and the protoplasts are almost exclusively 

 colored. I have obtained in this way very instructive 

 preparations of alcoholic material, adding to pretty thin 

 sections on the slide, after drying them externally with filter- 

 paper, a drop of the sulphuric acid containing the staining 



