ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 73 
phora and Clisetomorpha is also described ; it appears to be a mechanical 
contrivance for resisting traction. 
Propagation of Prasiola.* — Prof. G. v. Lagerheim describes two 
modes of propagation in a new variety of Prasiola mexicana. In ono 
mode certain cells become detached from the margin of the tballus, 
after the conversion of the intermediate membrane into mucilage, round 
themselves off, and directly reproduce the thallus. In the other mode 
the single layer of cells becomes divided by horizontal and vertical walls 
into one or two layers of four-celled sporanges. These four cells become 
free by the conversion into mucilage of the membrane of the mother- 
cell, and are motionless spores of irregular roundish, ovoid, rectangular, 
or triangular form. 
The second mode of reproduction presents strong analogies with the 
formation of tetraspores, and the author regards it as an argument in 
favour of the alliance of Prasiola with the Bangiacese, which he con- 
siders as directly derived from the Chlorophyeeae. He has observed 
pyrenoids with distinct crystalloids in the vegetative cells of Prasiola. 
Reproduction of Vaucheria.| — Prof. G. Klebs has investigated the 
various modes of sexual and non-sexual reproduction in Vaucheria 
sessilis. He finds that the zoospores themselves, or the germinating 
filament springing from the zoospores, may give rise either to zoospores 
again or to sexual organs, or they may remain sterile, the results varying 
according to the external conditions of nutriment, temperature, and 
light. Similar variable results were obtained from the culture of 
oosperms. As in Hydrodictyon, there is no regular alternation of 
generations. A powerful production of zoospores takes place when a 
vigorous tuft undergoes a change in its external conditions, whether 
from air into water or from running into stagnant water, or a great 
change in the amount of light. The conditions for the formation of the 
sexual organs are much more complicated than those for growth. A low 
temperature or a small amount of light will maintain a tuft in the 
sterile condition for an indefinite period. 
The formation of the sexual organs was found to obey the same laws 
in Vaucheria terrestris , hamata, geminata , uncinata , and aversa ; but the 
phenomena of non-sexual propagation differ in the different species. In 
V. terrestris and aversa there a, re no special organs for this mode ; 
V. geminata and uncinata produce motionless spores. V. clavata appears 
to differ from V. sessilis only in its physiological phenomena ; growing 
in rapidly running water, its sexual activity is greatly reduced, while the 
formation of zoospores is proportionately promoted. 
Fungi. 
Mastigochytrium, a new genus of Chytridiacege.J — Prof. G. v. 
Lagerheim describes under this name a new genus of Chytridiacese 
allied to Bhizophidium, with the following diagnosis : — Zoosporangia 
extramatricalia, sessilia, unicellularia, basi filamentis mycelicis radici- 
formibus ramosis, matrice immersis et pilis validis lateralibus instructa ; 
* Ber. Deutsch. Bot. Gesell., x. (1892) pp. 366-74 (1 pi.). 
t Yerhandl. Naturf. Gesell. Basel, x. p. 45. See Bot. Centralbl., li. (1892) 
p. 377. % Hedwigia, xxxi. (1892) pp. 185—9 (1 pi.). 
