1887.) MICROSCOPICAL JOURNAL. 23 
Lichen spores sown among alge germinated by sending out a tube, which 
by lateral branches soon came in contact with the alge. Following this 
union there ensued a more vigorous development of both the hyphez and 
algze which were connected, and, although in some of the experiments the 
observations extended over a period of some months, not the slightest indica- 
tion was found of a development of gonidia from hyphe. The same kind of 
lichen spores placed under conditions in every way the same, except that all 
alge were excluded, germinated by sending out hyphal tubes, but these soon 
ceased to grow, and died without having exhibited the least tendency to pro- 
duce gonidia. In some experiments spores were sown with the isolated go- 
nidia of another species of lichen, with the result that union took place and 
development proceeded as already described. 
These attempts at the synthesis of a lichen have been held to be inconclu- 
sive, since the innumerable difficulties of manipulation prevented the experi- 
menters from carrying their cultures along until well-developed fruiting lichens 
were produced. No such objection, however, can be urged against some 
cultures of Hxdocarpon pusillum made by Stahl. This lichen differs from 
those previously employed in the fact that it has, in addition to the gonidia 
found in its vegetative part, others scattered through the hymenium among the 
spore-sacs. These hymenial gonidia, as they are called, multiply in the 
hymenium, keeping pace with the development of the spores, and when the 
spores are ripe both spores and gonidia are ejected from the perithecium for 
some little distance, each spore being accompanied by several adhering gonidia. 
At the time of their ejection spores and gonidia were collected on a clean, 
moist surface and placed under conditions suitable for growth. Germination 
was seen to take place after the manner already described, and there was a 
similar union of hyphe with gonidia, and by careful management the cultures 
thus started were kept along until there was produced a fully-developed thallus 
of Hxdocarpon bearing spermagones and perithecia. 
It would surely seem that the evidence of such experiments, so ably con- 
ducted, ought to far outweigh in the minds of all botanists any amount of nega- 
tive results obtained by observers less skilled in such work and less trained in 
microscopy. 
There are writers who have expressed a difficulty in understanding on the 
dualists’ theory how it is that they find lichens so widely distributed on bare 
rocks, dead wood, and the like, while alge are pre-eminently aquatic. In 
the first place it may be said that alge are much more numerous in the situa- 
tions where lichens are found than these writers apparently suppose, and in 
the second place we have in lichens not only a reproduction by spores, but a 
multiplication by soredia (to be described presently), which throws much 
light on those cases where lichens are found in places unfrequented by alge. 
While it is, of course, a well-known fact that the great majority of algz 
live only in the water, still there are a certain number of common species 
which appear to have become well adapted to the frequent dry periods inci- 
dent to terrestrial life; and it is significant that these are the very species 
which the dualists recognize as forming lichen-gonidia. Such, for example, 
are species of Pleurococcus, Cystococcus, Stichococcus, Chrodlepus, PRiv- 
ularta, Vostoc, and other genera that might be added, and it is often an easy 
matter to collect specimens of these alge in the vicinity of lichens possessing 
them as gonidia. - 
As we have already said, the appearance of lichens in situations destitute 
of algee may well be accounted for as due to reproduction by soredia. These 
are minute protrusions at the surface of the thallus, often so numerous as to 
give it a powdery or granular appearance. Each soredium consists of a clus- 
ter of gonidia enveloped by hyphe, and, being very readily detached and so 
