296 . Lang . — The Prothallus 
present only be suggested as possibilities. The flattened and 
still more the trough-like form which these older prothalli 
present may be an adaptation to facilitate fertilization. 
Whether this be the case or not, it must, in cases where both 
kinds of sexual organs are present on the upper surface of the 
same prothallus, serve this purpose by arresting the water 
percolating through the peaty soil and causing it to run over 
the surface of the prothallus before sinking deeper. The 
complete absence of chlorophyll shows that the prothallus is 
a total saprophyte, and, as is almost invariably the case in the 
higher plants, a Fungus is found living as a symbiont in the 
tissues. The few prothalli found did not unfortunately permit 
of a determination of the relation which the two organisms 
bear to one another ; such a comparatively simple example 
of mycorhiza presents a problem of great interest. We may 
however assume with probability that the Fungus acts in 
some way as an intermediary in rendering the organic 
material, absorbed from the soil by the numerous rhizoids, 
and possibly by the hyphae which extend to the soil ; avail- 
able as food for the prothallus. The appearance of the 
mycelium in different regions of the prothallus further 
indicates that at a certain stage the whole of the contents of 
the Fungus are made use of by its host. Since the young 
plant is not inhabited by the Fungus, it must be wholly 
dependent on the prothallus until it reaches the light. This, 
owing to the depth at which the prothalli grew, does not take 
place until the plant has attained a considerable size, a fact 
which may be put in relation with the large foot which the 
embryo possesses. 
Comparative Remarks. 
In this portion of the paper an attempt will be made to 
gather together the facts that are known regarding the 
gametophyte of Lycopodium , and to consider their bearing on 
the relationship of the species included in that genus to one 
another and to other groups of Vascular Cryptogams. The 
full account of the prothallus of a number of European 
