SCIENTIFIC SUMMARY. 
363 
generally zoospores, each of which of itself (or when a copulation takes 
place the product of this process) grows into an individual like the parent 
cell. In external form and internal structure, these Algae are very similar ; 
the principal differences between them are manifested in the particular 
features of the development, and especially in sexual fertilization. One of 
them, Scotinosphcera parodoxa, is decidedly asexual, if a two years’ culti- 
vation may he decisive upon this point; this Alga possesses a special 
peculiarity, the structure of the constantly asexual zoospores. The cell, at 
its maturity, shows a differentiation of the green protoplasm into numerous 
cylindrical rods ; these gradually fuse together, during which process a red 
plasmatic granular matter is separated. The final result is the formation of 
a single dark-green sphere in the midst of the red granular matter ; this 
sphere immediately begins to divide again, and by repeated divisions, during 
which the red matter is again taken up, the asexual zoospores are produced. 
The simplest process of sexual fertilization is exhibited by two other 
Algae, Chlorochytrium Lemnce and Endosphcera biennis. In these the zoo- 
spores, which are produced simply by repeated binary division, always 
conjugate in pairs, which originate from the same mother-cell; only the 
product thus formed is capable of propagating the species. In Chlorochy- 
trium, in the course of the summer many of these sexual generations are 
successively produced, and the generation first exposed to the influence of 
winter falls into a resting state ; in Endosphcera, on the contrary, each 
generation requires a whole year for its development. This simplest 
possible form of reproduction by self-fecundation was previously known 
only in Actinosphcerium Eichhornii. 
A perceptible differentiation of the two conjugating sexual cells makes 
its appearance in Phyllobium dimorphum , which lives during the summer 
in the leaves of Lysimachia nummularia , in the form of green branching 
tubes. Some of the cells form large, and the others small zoospores, and 
only the product of the conjugation of a large one with a small one is 
susceptible of development. Some other peculiarities occur, which show 
upon how low a grade of development the several phenomena are in these 
green unicellular Algae ; nay, even their constancy in the same species, or at 
any rate in very nearly allied forms, is but slight. In the genus Chlorochy- 
trium , besides the distinctly sexual species, C. Lemnce , there are other 
species in which the course of development is otherwise exactly the same, 
but the zoospores never conjugate; each of them is capable of continuing 
the species. In Phyllobium , also, species are known (one of them is 
described as P. incertum) which are reproduced only by asexual zoospores, 
and it is interesting to find that the decidedly sexual P. dimorphum may 
also, under certain circumstances, lose its sexuality, and become an asexually 
reproductive form. 
The Algae described have one biological peculiarity in common, — they do 
not live in the water but in other plants, some in dead, some in dying, and 
some only in living parts. The author does not think that these and similar 
• Algae can be regarded as parasites, but that the plants merely seek shelter 
within the organisms they infest. 
