1 6 7 
the Prothallus of Equisetum debile , Roxb. 
quite small and simple at first. As these cells grow they become divided 
by transverse and vertical walls, and more cells from the side of these rudi- 
mentary lobes begin to grow vigorously and project outwards. Thus the 
lobes become branched, and although united at their bases to the main 
body of the prothallus (as yet only the cell-mass more or less changed by 
this time) and to each other, they are quite free above (Figs. 14, 15). Soon 
the cells at the base of all the lobes begin to divide so that they contribute 
to the tissue of the cell-mass below and form new lobes above. Thus the 
structure of the mature prothallus is established. 
Numerous prothalli were found growing wild on the river bank, less 
than one millimetre in diameter, looking like green or red pin-heads. Even 
at this stage they have the same essential structure as the large prothalli of 
a diameter of 3 centimetres. They are minute hemispherical cushions con- 
sisting of compact parenchymatous tissue in their lower half, and of perfectly 
erect lobes, with narrow spaces between them, in their upper half. A very good 
idea of their structure can be obtained by saying that they resemble 
miniature cauliflowers without the surrounding leaves. The prothallus is 
firmly fixed to the soil by numerous rhizoids. The rhizoids are so numerous 
and so firmly attached to the mud that it is very difficult to wash it away, 
and usually most of the rhizoids are removed during the operation. The 
rhizoids are smooth long hyaline unicellular structures and do not present 
any peculiarity. 
At a stage when the diameter of the hemispherical prothallus is about 
| to J of an inch (3 to 6 millimetres) it is usually of a circular outline with 
an entire margin (Fig. 16 b). Often, however, the outline is cordate or 
reniform with a notch on the posterior end, probably due to the manner of 
cell-division in the early stages. When a cell-mass has given rise to the 
prothallus directly, the outline naturally would be circular, as the meristem 
is developed uniformly on all sides. If the prothallus is formed after the 
formation of filaments or a ‘ primary tubercle the meristem arises late on 
the posterior end and has a reniform or cordate outline (Figs. 1 6 a, 17). 
There is, however, no trace of the ‘ primary tubercle ’ in the older stages. 
