14 HOFFMANN ON THE CIRCULATION 



sheath of a leaf (like the scale of a bulb), which was especially 

 rich in sap and reacted strongly, while at the lower part of the 

 stem this part was already dead and in a great measure decayed 

 away. In this sheathing base of a leaf the elongated cells had 

 chiefly absorbed the salt, while the liber bundles were not dis- 

 coloured. The principal mass of the vessels (their walls present 

 short streaks) lie in some degree concentrically, at equal distances 

 from the centre and the circumference ; the vascular bundles, 

 with their woody envelopes, contained air and were not disco- 

 loured 5 but in the rounded, four-sided, starchy parenchyma cells 

 between them, blue points were observed, which occurred in 

 proportionately largest quantity in the vicinity of the central 

 point and of the periphery. In a longitudinal section it was seen 

 that the reacting cells exhibited scattered points or little streaks, 

 and never lines continued in one plane. The vascular bundles 

 run pretty nearly parallel in the stem ; even the nodes exert no 

 influence upon the arrangement of the internal parts lying 

 opposite to them. When the stem was cut through higher up, 

 where it begins to lose itself in the leaves, a different appearance 

 was seen. Yet microscopical examination showed that here 

 again the salt had not ascended inside the vessels, but only in 

 their immediate neighbourhood, inside the elongated cells by 

 which they are accompanied. The upper leafy, as well as the 

 peripherical, parts of this plant reacted far more strongly than 

 the interior of the stem. 



Commelina ccelestis, Willd. (Commelineae). — This plant was 

 watered on the I7th of July; the examination was made on the 

 24th and 26th of July, and the 9th and 15th of August, but in 

 all cases the salt was sought in vain in the parts of the stem 

 situated between the nodes, while in the nodes themselves, from 

 the lowest to the uppermost, the reaction could be easily de- 

 tected. From this it appears, taking the other experiments into 

 account, that we must conclude the sap to rest for a time in 

 particular parts of plants, as in tubers, nodes, buds and ovaries, 

 while it hurries rapidly through others, especially the internodes 

 of the stem. The cross section of the nodes of the stem exhibits 

 a distinct separation into pith and rind. The bundles of spiral 

 vessels, which displayed bubbles of air in their interior when ex- 

 amined with the microscope, exist both in the pith and the 



