204 ~ Transactions. 



cells, some of which have divided. Outside this again is another single 

 layer of somewhat smaller cells which may or may not contain the fungus, 

 boimded peripherally by the epidermal layer, whose external walls are 

 cuticularized. These same layers can also be distinguished in fig. 22 in 

 longitudinal section. Thinner branches show less cell-multiplication in the 

 fungal zone. In longitudinal section it is apparent that the fungus- 

 containing cells have divided transversely, so that they are more nearly 

 equidimensional than those either of the central strand or of the epidermis. 

 The fungus ii present in the form of hyphal coils or clusters of oval dark- 

 staining " spores." The fimgus also extends between the cells, so that the 

 latter are frequently roundish in shape. 



Sooner or later a branch will show a thickening of its tissues at the apex, 

 and on this swollen region paraphyses and sexual organs will arise (figs. 6, 

 23, 24)_. Such a swollen region will be free from the fungus, but the hyphal 

 coils are often aggregated very thickly in that portion of the branch' which 

 lies immediately behind it (fig. 24). It is always antheridia which are first 

 formed in such branches, the archegonia occurring only on the main central 

 region of a prothallus. However, a branch may thicken and develop to 

 such an extent that it practically becomes a new prothallus. Probably not 

 a few mature prothalli have arisen not from the germination of a spore, 

 but by a branch having become detached from an older prothallus and 

 having gone on growing in thickness. Such a branch will put forth lateral 

 branches, and will eventually bear archegonia as well as antheridia on its 

 main body. This will account for the fact that most of the mature pro- 

 thalli found by me did not show the typical cone-like basal region. They 

 are in fact prothalli which have arisen adventitiously. Fig. 27 shows in 

 external view the terminal region of a stoutish branch of L. Billardieri var. 

 gracile which has begun to develop antheridia and paraphyses. Some of 

 the detached branches which are dissected out of the humus are imperfect 

 at both extremities, a fact which indicates that they may persist in the 

 humus and remain self -nourishing for a considerable time. 



In dissecting out prothalli of these species of Lycopodium from the sub- 

 stratum in which they lie, one frequently comes across detached prothallial 

 branches which have probably arisen by the decaying-away of the parent 

 prothallus. Three such branches of L. Billardieri var. gracile are shown in 

 figs. 28-30. In this particular species these branches are frequently very 

 long and thin, and they may show the presence of paraphyses along 

 extended portions of their length. Lateral branches frequently 'bear short 

 club-shaped processes, sometimes in great numbers (fig. 30), which are 

 quite dark with the fungal inhabitant. These processes are to be regarded 

 as " resting " processes, and they may occur also on mature prothalli of 

 the ordinary kind (figs. 1, 11). They are frequently met with detached in 

 the humus, and are either of a simple nature or are branched (figs. 8, 25). 

 The actual apex of the resting process is white and clear of fungus, but the 

 rest is very dark, being thickly infested with it. Fig. 31 represents such 

 a resting process in transverse section, from which it will be seen that the 

 central cells contain the fungus as well as those more medianly situated, 

 and that the fungus is intercellular as well as intracellular. The apex of 

 one of the branches of the stout 'resting process shown in fig. 25 is given 

 in longitudinal section in fig. 32. Immediately behind the apex the fungus 

 is hyphal only and does not penetrate between the cells. Farther back, 

 however, the hyphal coils have to a large extent been replaced by the 

 " spores," and the fungus is also intercellular. Instances may be met with 



