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of Lycopodium clavatum , A. 
rudimentary or entirely absent. Thus, in the fully developed 
prothallus of this type, three regions can be more or less 
clearly distinguished : the primary tubercle, the cylindrical 
portion, and the terminal region bearing the sexual organs 
and assimilating lobes. Since development proceeds from 
a zone between the two latter regions, the youngest lobes 
and sexual organs are to be found towards the periphery 
next the meristem. 
The structure of the prothallus is very simple, and exhibits 
little differentiation of tissues. Chlorophyll is most abundantly 
present in the terminal lobes and the upper portion of the 
cylindrical part, while the rhizoids are borne on the lower 
portion of the latter. The more internal cells are somewhat 
longer than those of the superficial tissue, but are not markedly 
elongated in the direction of the longitudinal axis. An endo- 
phytic Fungus is almost constantly present ; this occupies 
the cavities of the outer cells of the primary tubercle, and 
extends between the internal cells of this region and into 
the cylindrical portion. Both antheridia and archegonia take 
origin from a single superficial cell. The former hardly pro- 
ject from the surface of the prothallus, and the free portion 
of their wall presents a triangular cover-cell. The spermato- 
zoids developed from the large mass of spermatocytes are 
biciliate. The mature archegonium consists of a short pro- 
jecting neck of four rows of cells, and of the central series 
of ovum, ventral canal-cell, and a single neck canal-cell. 
The embryo at an early stage consists of the suspensor, 
which usually remains unicellular, and of two tiers of cells 
borne on this. The small foot proceeds from the whole of 
the tier adjoining the suspensor ; the terminal tier gives origin 
to a small tuber-like structure (the protocorm), which becomes 
attached to the soil by numerous rhizoids, and to the first 
leaf. As the protocorm develops, other leaves of simple 
form and structure are produced from it. Not until a number 
of these have appeared is the apex of the stem differentiated ; 
this grows into the leafy shoot of the Lycopodium plant, the 
first root arising exogenously from the protocorm near to it. 
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