ELIMINATION 191 



Leaf-clasp Chambers. For applying the cobalt-chloride discs to the 

 leaf while protecting them from the moisture of the air, Stahl used little 

 sheets of mica held in place ty clamps; and where the leaf was very rough, 

 he sealed the edges by a special wax. An excellent modification of this,, 

 using glass slips, is given Ly Linsbauer, 38. For greater accuracy and con 

 venience of application of this test, as well as for some allied uses, I have 

 devised a special leaf clasp originally described in the Eotanical Gazette, 

 39, 1905, 148, which is among my normal apparatus (page 46) and con- 

 structed as follows: 



Two similar brass rings (Fig. 51), "chamber rings," each 30 mm. in 

 diameter and 3 mm. in depth, are attached at the ends of parallel flexible- 

 elastic bars, so arranged that they hold the rings firmly and exactly edge to 

 edge, while allowing of their separation, by means of a screw, to any desired 

 extent. A second screw permits of their tighter closing, while manipula- 



Fig. 51. — Leap clasp; Xf. 



tion of the two screws together allows a certain amount of adjustment of the 

 rings to fit surfaces not in the same plane. For each chamber ring there 

 are provided two accessory rings. One of these is right-angled in section 

 and holds a removable cover-glass, so that when pushed over the outer edge 

 of the chamber ring, it converts the latter into a glass-topped chamber, as 

 shown in the figure. If discs of filter-paper treated with cobalt chloride 

 are so placed in the chambers as to rest against the leaf, their change of 

 color in transpiration may be observed with the greatest clearness and facility. 

 Incidentally the tightness of the chambers (when not on the leaf) permits the 

 papers to retain their dryness and blue color for a considerable time, so 

 there is no need of haste in applying them to, the plant. The second acces- 

 sory ring is broken, and is intended to hold paper, rubber, or other fabric 

 tightly to the chamber ring either inside or outside thereof. Thus if pro- 

 jecting veins prevent a connection of chamber with leaf sufficiently tight 

 for some special purposes, a band of thin rubber may be held by the broken 

 ring in such a way that it will project against the leaf, filling the spaces be- 

 tween the veins. The discs can be so held in place, by flaps under the 

 broken rings inside the chamber, that they need not thereafter be removed, 



