38 HOFFMANN ON THE CIRCULATION 



fluid is here spread about too much and too unequally ; hence 

 the absorption becomes very uncertain, or even fails to take 

 place at all^ as I have experienced several times to my dis- 

 comfort in vines^ plums, and sycamore trees. I therefore pre- 

 ferred such plants as had been kept a longish time in pots, 

 taking only such as exhibited a full activity of vegetation. 



Euphorbia terracina, L. — Watered on the 5th of June ; taken 

 up by the root on the 8th. The saline solution was detected in 

 the inner layer of the bark (the liber), and in a few tracheae or 

 spiroids of the outer layer of wood. Watered on the 15th ; 

 withering on the 24th ; taken up on the 25th ; the saline solu- 

 tion could be detected last, as far as 2^ inches above the collar of 

 the root, in the striped spiroids of the outer layer of wood and 

 in the liber, in which it ascended farthest. These vessels were 

 only partially filled with the saline solution ; the majority still 

 contained air and did not react. 



Since in these and several similar cases, not only the cellular 

 tissue, but also — in direct opposition to the preceding observa- 

 tions on the Monocotyledons — the air-vessels took part more or 

 less in the conduction of the sap, the first object was to clear up 

 the contradiction. 



The Monocotyledons used in my investigations, whatever 

 their other differences, w^ere almost without exception furnished 

 w^ith tuberous or bulbous rhizomes. The conjecture was not 

 far-fetched, that the predominant subterraneous stem-structure, 

 the whole character of which is, moreover, accumulative and 

 retentive, retarded the conveyance of the fluid into the upper 

 portions of the stem, and thereby exerted essential influence 

 over it. Hence arose the question, whether, in the Dicoty- 

 ledons also, varied conditions in the conduction of the sap 

 would occur according to the rapidity of the absorption, accord- 

 ing to superabundant or scanty watering, &c. 



a. Accelerated absorption of the Fluid. 

 Balsamina hortemis. — The root was carefully freed from earth 

 and immersed in a large vessel full of solution of the ferrocy- 

 anide ; then the stem was cut across obliquely at a height of 

 8 inches, and sucked with the mouth. After the sucking had 

 been continued for half an hour, reaction occurred at this point ; 



