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the Prothallus of Equisetum debile , Roxb. 
On account of the ventral position of the meristem the young lobes are 
directed obliquely forwards and upwards, but are soon carried upwards and 
become perfectly erect. 
The upper surface of a comparatively small prothallus has the form 
shown in Fig. 22 ; it is quite smooth and slopes down gradually towards the 
margin, but in large prothalli furrows and ridges appear on the surface 
(Fig. 18) partly owing to the unequal height of the lobes and partly to the 
inequalities of the soil. These furrows are, however, quite superficial. 
The margin of the prothallus is quite entire in small prothalli 
(Figs. 16 a and 1 6 b), but as the prothallus increases in size the whole body 
of the prothallus becomes lobed. This is chiefly due to mechanical reasons, 
as the prothallus in its advance comes into contact with foreign bodies which 
interfere with the growth. Moss plants were often found in the fissures 
between these lobes of the prothallus ; also a compact form of Riccia 
crystallina , which is extremely common on the river-side, and similar 
bodies. The prothallus may have an inherent tendency to divide, but it 
cannot be definitely stated as regards this species. According to Campbell 
dichotomy of the archegonial meristem does occur in prothalli of other 
species (‘ Mosses and Ferns/ p. 453). Although the first cleft was found 
in many cases in the median line in many heart-shaped prothalli, this 
was not always the case. Two such fissures are shown in Fig. 17. The 
margin of the prothallus on the two sides of the fissure are in intimate 
contact with each other, so that there is hardly any space between them. 
The existence of these fissures cannot be detected from an examination of 
the prothallus from above ; in most cases it is necessary to wash away the 
mud from the ventral surface to demonstrate their presence. 
Looked at from above the prothallus appears merely to be spongy, and 
one would not suspect the existence of separate lobes inside, so closely 
together are they situated. This compactness, however, varies to some 
extent with external conditions. The colour of the prothallus also varies 
similarly. If the prothallus grows in an exposed place directly exposed to 
intense light, it is invariably compact and red in colour. (If one part of the 
prothallus is exposed to direct sunlight and the other shaded — e. g. if the 
prothallus happens to be growing in a pit obliquely — the two colours may 
be seen in the same prothallus.) There is absolutely no trace of the lobes 
from the surface. The red colour is due to the presence of a pigment in 
the numerous chloroplasts of the upper cells of the lobes in addition to 
chlorophyll. The red colour easily comes out if the prothallus is placed in 
absolute alcohol, while chlorophyll remains in the chloroplasts for a much 
longer time. The pigment is probably a decomposition- product of 
chlorophyll. If the prothallus grows in a shaded place under some tree 
or in some small pit, or if it is kept in the laboratory, it is always of a 
bright green colour and less compact. If a compact prothallus of a red 
