General Form of the Prothallus.
The complete mature prothallus of all these three New Zealand forms, similarly to those of the four tropical epiphytic species described by Treub, consists essentially of a central body of tissue, which may be either bulky or more or less elongated, and a number of branches which arise adventitiously from this central body. In fig. 1 is shown such a complete mature prothallus of L. Billardieri var. gracile in external view, the natural size being also indicated in the illustration. The central body of the prothallus as here shown is somewhat slender and elongated, a condition which I have found generally to be the rule in this variety. It possesses two complete, and also two broken, thin vegetative branches; a young, stouter branch; and also, nearer the forward end, a short club-shaped “resting” process. The two complete branches on the left side of the figure have begun to put forth secondary branches, while one has also commenced to expand at its growing end preparatory to there bearing sexual organs. The oldest end of the prothallus is intact, and shows clearly the original cone form with which the prothallus of the epiphytic type always begins. At the apex of the cone the cell first formed from the spore still persists. The main prothallial body shows the presence of fungus in its internal tissues, this fungal inhabitant occupying the whole of the tissues in the dark basal cone-like region, but being more irregularly distributed farther forward. The fungus is also present in the vegetative branches, being there also somewhat irregularly distributed, and the single club-shaped resting process is very dark with it. The ends of the branches are all quite free of fungus and are translucent in appearance. The forward end of the main prothallial body is slightly more bulky than the rest, and is quite clear of the fungus. This is the main generative region of the prothallus, and bears paraphyses, archegonia, and also a young plant. The whole prothallus is covered with long rhizoids inclining forward towards the growing apices, except on the terminal bulky region, which is wholly devoid of them, and on the basal cone-like region, from which they have decayed away, leaving only short, stubby projections. The description of this particular prothallus in its external
appearance will suffice to illustrate the general features of the three New Zealand epiphytic species here dealt with.
L. Billardieri var. gracile grows abundantly throughout Westland on stems of the tree-fern Dicksonia squarrosa, and it has also been reported from various other parts of New Zealand in the same situation. The
Fig. 1.—L. Billardieri var. gracile. Complete mature prothallus in general view, showing basal cone intact, lateral branches, and plantlet. × 13. The small figure represents this prothallus at ¾ natural size.
prothalli and young plants occur more especially on the younger stems of the Dicksonia in between the bases of the stipites, which in this tree-fern run down the stem a considerable length before they begin to be overgrown by the mass of hard brittle aerial rootlets. It is in this more open part
of the tree-fern stem-surface that the prothalli and plantlets of both L. Billardieri var. gracile and of Tmesipteris occur. As the tree-fern grows in height the covering of aerial rootlets spreads up the stem, and so plantlets of increasing age have to be carefully dissected out from the mass of the brittle rootlets. The prothalli of this species of Lycopodium are often to be found adhering closely to the hard black surfaces of the stipites, and are there readily found by tearing away the humus and the debris of old tomentum which collects between the bases of the stipites. Their rather delicate, attenuated form is probably the result of this particular position of growth.
Fig. 6.—L. varium. Prothallus in general view, showing central body and branches, and a young plant. × 10.
Fig. 7.—L. varium. Prothallus in general view, showing basal end, and young embryo in the generative region. × 10.
Fig. 8.—L. varium. A branched “resting” process in general view. × 10.
The prothalli of L. Billardieri, on the other hand, occur for the most part in masses of humus on elevated positions in the forks of the forest trees and of their main branches. The central prothallial body is generally more bulky than that of L. Billiardieri var. gracile, but otherwise the prothallus is identical both in appearance and in structure. With regard to the tropical forms studied by him, Treub states that the prothalli of L. Hippuris are much larger and thicker than-those of L. Phlegmaria, while those of L. nummularifolium are exceedingly thin. These epiphytic prothalli have very much the appearance of a mass of root-ends, but a little
experience in dissecting soon leads one to detect the presence of a central region and so distinguish the prothalli from rootlets. Moreover, the root-ends and vegetable fibres so commonly to be met with in the humus are more dead-white or yellowish in appearance, the prothalli in their fungus-free regions being somewhat translucent. Figs. 2–5 show the central bulky region of four prothalli of L. Billardieri, from all of which the oldest basal region is absent. The distribution of the fungus is indicated in these figures by dark shading. It will be seen that the forward region of the central prothallial body is the most bulky, and is wholly free from fungus. It is also quite devoid of rhizoids. It bears on one surface—the upper—paraphyses in large numbers, and also sexual organs. The archegonia and antheridia are not intermingled, but occur in clearly defined zones arising immediately behind the growing apex of the prothallus. The surface appearance of an old antheridium is shown in fig. 3a, the triangular opercular cell being a very distinct feature. The under-surface of the generative portion of the prothallus is always quite naked and smooth.
Lycopodium varium is closely allied to L. Billardieri, but grows terrestrially and has a somewhat different habit of growth. Its prothalli are in every respect identical with those of L. Billardieri. Three prothalli are shown in figs. 6–8. That in fig. 6 bears a young plant; its basal end is not seen. That in fig. 7 shows the basal end dark and withered, and a very young embryo can be seen through the tissues of the forward generative region. In fig. 8 is shown a branched “resting” process. In none of these figures is the distribution of the fungus indicated.