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LICHEN HYPHAE . 47
a few spores were abstracted from the culture and examined microscopically.
Tulasne observed that the spore did not increase or change in volume in the
process of germination, but that gradually the contents passed out into the
growing hyphae, till finally a thin membrane only was left and still persisted
after two months (Fig. 14). For a considerable time there was no septation ;
at length cross-divisions were formed, at first close to the spore, and then
later in the branches. The hyphae meanwhile increased in dimension, the
cells becoming rounder and somewhat wider, though always more slender
than the spore which had given rise to them. In time a felted tissue was
formed with here and there certain cells, filled with green colouring matter,
similar to the gonidia of the lichen and thus the early stages at least of a
new thallus were observed. The green cells, we now know, must have gained
entrance to the culture from the air, or they may have been introduced with
the water.
B. DEVELOPMENT OF LICHENOID HYPHAE
Lichen hyphae are usually thick-walled, thus differing from those of fungi
generally, in which the membranes, as a rule, remain comparatively thin.
This character was adduced by the so-called "autonomous" school as a proof
of the fundamental distinction between the hyphal elements of the two
groups of plants. It can, however, easily be observed that, in the early
stages of germination, the lichen hyphae, as they issue from the spore, are
thin-walled and exactly comparable with those of fungi. Growth is apical,
and septation and branching arise exactly as in fungi, and, in certain circum-
stances, anastomosis takes place between converging filaments. But if algae
are present in the -culture the peculiar lichen characteristics very soon
appear.
Bonnier 1 who ,
made a large series of synthetic cultures, distinguishes
three types of growth in lichenoid hyphae (Fig. 15):
1. Clasping filaments, repeatedly branched, which attach and surround
the algae.
2. Filaments with rather short swollen cells which ultimately form the
hyphal tissues of cortex and medulla.
3. Searching filaments which elongate towards the periphery and go to
the encounter of new algae.
In five days after germination of the spores, the clasping hyphae had
laid hold of the algae which meanwhile had increased by division; the
swollen cells had begun to branch out and ten days later a differentiation
of tissue was already apparent. The searching filaments had increased in
number and length, and anastomosis between them had taken place when
1 Bonnier i88q 2 .