176 The Anatomy of Plants BOOKII 



later and was made the subject of very careful investiga- 

 tion by several observers, very largely under the influence 

 of Sachs, who laid great stress on the importance of such 

 a relationship. Fromman in 1880 believed he had been 

 able to trace it, while Tangl in 1879 and 1880 also occupied 

 himself with the problem. The chief obstacle to the study 

 of the minute histology of the tissues was the inadequacy of 

 the methods which were in use. Those which were applicable 

 to the problem of continuity were confined to swelling up 

 the walls with sulphuric acid and subsequently staining with 

 iodine. Such treatment was moderately successful with the 

 coarse elements of the sieve tube, but was utterly useless with 

 the delicate cell walls of the greater portion of the plant. 

 Gardiner undertook an investigation at the instance of 

 Sachs in 1882, and was successful in so far modifying the 

 methods in vogue as to enable him to investigate the more 

 delicate tissues. Russow was engaged in similar investiga- 

 tions simultaneously, his work following his study of the 

 sieve tubes. 



Both observers modified the swelling reagent so as to 

 bring the swelling about more gently, and thereby to avoid 

 the destruction of the delicate threads ; having it under 

 control they stained the tissue with various aniline dyes. 

 Gardiner treated it with iodine before swelling the wall, 

 and used a further fixing reagent, picric acid, in conjunction 

 with his stains. Both published their researches in 1883. 

 Gardiner was successful in demonstrating the continuity 

 of the protoplasm in the cells of the endosperm of various 

 seeds, and in ascertaining many facts about the arrange- 

 ment of the connecting threads. He was led to the opinion 

 that such communication is general, but he considered he 

 had not satisfactorily demonstrated it. 



Russow claimed that he had demonstrated the existence 

 of the threads in a variety of tissues, including such delicate 

 cells as those of the cambium. 



