376 



MANIPULATION. 



Fig. 247. 



In order to do this, the phiiil holder previously described at 

 page 143 will be necessary; into the tube, 

 as there shown, the phial, previously well 

 corked, must be placed with the plant oppo- 

 site the hole, the holder is now to be fixed 

 to the stage of the microscope, and the light 

 reflected through the bottom tube, when the 

 Chara may be viewed in the same manner as 

 any other object. In order to get any part 

 in particular into the field of view, the phial 

 may be either turned round or slid in and 

 out, the spring in the dark chamber will 

 always keep it firmly pressed against the 

 upper part of the tube through which it is 

 passed. This mode of treating the Chara 

 has many advantages, not only is it always ready at hand, 

 but the growth of any particular part can be watched from 

 day to day, as the small specimens will frequently keep alive 

 for many months when not exposed to too much light, and 

 the water changed occasionally. Mr. Varley has contrived a 

 microscope for the express purpose of holding the phial ; this 

 instrument is fully described in the fiftieth volume of the 

 Transactions of the Society of Arts, and will be found exceed- 

 ingly useful to those about to investigate this very interesting 

 subject. 



Soon after the circulation in the Chara and the Nitella had 

 become generally known, the attention of microscopists was 

 directed to discover the same phenomenon in other plants ; 

 amongst the first that yielded to a careful scrutiny was the 

 Hydrocharis morsus ranee, or Frog-bit, an aquatic plant very 

 common in ditches and streams. Mr. Slack has given an 

 excellent account of it in the forty-ninth volume of the Trans- 

 actions of the Society of Arts, from which figs. 248 and 249 are 

 taken. Fig. 248, a, represents a portion of the plant of the 

 natural size ; surrounding the leaf-buds, b, are very transpa- 

 rent scales, as seen at c, in these the circulation may be 

 observed by placing them upon a glass slide with water, and 

 laying a thin glass cover over them ; when viewed with a 



