OF ARTS AND SCIENCES. 121 



EXPLANATION OF THE PLATE. 



All the figures are of Champia parvula. Fig. 2 is from a free-hand section 

 mounted in glycerine and acetic acid. It is drawn chiefly with the camera- 

 lucida, but in places is slightly diagrammatic. The other figures are strictly 

 camera-lucida drawings. Those beyond Fig. 2 are made from stained micro- 

 tome sections mounted in benzol balsam. 



Fig. 1. A small branch, with a portion of the larger one from which it 

 sprang. X -j 1 . 



Fig. 2. Interior view of the upper portion of a branch, a, apex ; 6, bulb-cell; 

 c, cortex ; d, diaphragm ; f. filament ; e, connection between the filament and 

 the cortex. X - L l-- 



Fig. 3. Longitudinal section of a tip passing through the apex, a, apical 

 cell ; the other letters as above. X 2 ^ s ~- 



Figs. 4-10. A series of transverse sections from a single tip. They are about 

 5fj. thick. Figs. 4-7 are a continuous series, Fig. 4 being the extreme tip. Figs. 

 8 and 9 are the sixth and seventh sections of the series, and Fig. 10 is the tenth. 

 Figs 4, 5, and 6 show the converging rows of cells, each headed by an apical cell. 

 In Fig. 7 we get the beginning of the cavity. Fig. 8 shows the condition just 

 above the young diaphragm, which appears in Fig. 9. Fig. 10 is the first section 

 that cleared the diaphragm below. By comparing with Fig. 3, it will be seen that 

 these sections are oblique to the axis of all the cells in them, except those very 

 near to the middle of the section. 1, 2, 3, etc., indicate corresponding areas in 

 the different sections. X ^f-- 



Fig. 12. Transverse section of another branch through the third diaphragm. 



Fig. 11. Second section above Fig. 12. In these two sections we have very 

 nearly the adult condition. X ^f 2 -. 



