412 



any bubbles rise from (lie water. Wlien (lie connections are made 

 with vacunin iMiblier-tuhe and glass to glass, leakages do not occur. 



11. 



Descriptions of' tiie parts. 

 (I. Sucking- and forcinff-piimp (fig. 2). 



An air-light |)mn|), working for a long period witliont failing and 

 having a sufficient capacity, is easily constructed. 



• The glass tubes / and ii are connected by a piece of strong 

 rubber-tulie p (about 15 cms. long and 2'/. cms. wide). Each of the 

 tubes / and /i is |)rovided with a valve, consisting of a piece of 

 vacuum-tube (1 cm. long) 1, to which the end of a piece of valve- 

 tube 2 (about 3 cms. long) is glued on with solution. The other 

 end of the valve-tube is tightly tied with a string at 3; in the 

 valve-tube a straight lengthwise cut 4 is made, the two edges of 

 which meet, when the pump does not work. To prevent these edges 

 from sticking together afterwards, they have been rubbed in with 

 talcum powder. The glass tubes / and v fit in the rubber-tube ji, 

 while the vacuumpieces 1 must also fit jierfectly. How the pump 

 works, when the hammer h taps on it, is clear from the fig. 2. 



6. The respiratory-vessel (fig. 3). 



As in Kuyper's research') here too is made use of a copper 

 cylinder 1. The experimental objects are on the ebonite plates t, 

 fixed to an axis a,. In each of the plates i 25 round holes are 

 made in such a way, that germinating seeds of Pisum sativum 

 cannot fall through. On the plates t^ moist cotton-wool is put, on 

 which the roots rest, in consequence of which there cannot occur 

 a deficiency of water. The axis (/, is enlarged at the top, provided 



1) KuYPER J: Recueil des Travaux Botaniques Néerlandais. Vol. VII. 1910, pag. 1. 



