ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
217 
of the oospore the nucleus of the zygote undergoes direct division to 
furnish one nucleus for each zoospore. 
In conclusion the author advocates the view that the sporophytc 
generation of the higher plants probably owes its origin to the fusion 
of gametes whose nuclei did not undergo a reducing division. The 
doubling of the chromosomes acted as a stimulus to spore-formation, and 
involves a halving of the chromosomes in the return from the undoubled 
condition of the nuclei in the gametophyte generation. 
Commenting on this paper, Prof. M. Hartog * charges the author 
with several erroneous conclusions. In particular he states that he has 
overlooked the existence of four chromosomes in the vegetative nuclei, 
to which he ascribes only a single chromosome. 
Infection of TJstilaginese.f — Prof. 0. Brefeld publishes the result 
of a series of observations of the infection of their respective host- 
plants by the parasitic species of Ustilagineae, especially of Ustilago 
Avense on Avena sativa, TJ. cruenta on Sorghum saccharatum, and 
U. Maydis on Zea Mays. The saprophytic stage of the development of 
these parasites is especially dwelt on. It presents two different forms 
in two different groups. In one (U. longissima, grandis. and bromivora ), 
the conids give birth in the nutrient solution again to conidiopliores ; 
in the other group (U. carbo, Maydis , and cruenta ), the conids ait) 
developed directly from the preceding generation of conids. 
It was found, in the infection both of oat and barley by TJ. carbo, and 
of Sorghum saccharatum by TJ. cruenta , that the seedlings are most recep- 
tive to infection in their earliest stages of germination, the susceptibility 
gradually decreasing as the tissues become more differentiated. The mix- 
ing of the soil with fresh horse-dung greatly facilitates the infection. In 
the cases of TJ. carbo and TJ. cruenta infection can take place beneath 
the surface of the soil ; while with TJ. Maydis infection is carried through 
the air by the conids, which, however, are produced from the ustilago- 
spores only in nutrient solutions (saprophytically). The ustilagospores 
themselves are inoperative in infection. The action of the infection- 
germ is strictly limited locally to the tissues in the immediate neigh- 
bourhood of the spot where the germ has entered. 
Morphology of the Lichen-Thallus.J — Dealing further with this 
subject in great detail, Prof. J. Keinke’s present instalment of his trea- 
tise includes the Parmeliaceae and Verrucariaceee ; the structure of the 
thallus is described for a very large number of species. The Parme- 
liacem are derived, by further development, from the Lecideacem. Some 
of the families have chlorophyll-green, others blue-green gonids. The 
Omphalariese exhibit a great variation in the structure of the fructifica- 
tion, from a discocarp tea pyrenocarp ; but they must not, for this 
reason, be distributed among the Discolichenes and the Pyrenolichenes. 
The Verrucariaceee are probably derived from the Sphaeriacese. They 
* Op. cit., x. (1896) pp. 98-100. 
t ‘ Unters. a. d. Gesammtgeb. d. Morph. ; Heft xi. Die Brandpilze,’ Miinchen, 
1895, 98 pp. and 5 pis. See Bot. Centralbl., lxiv. (1895) p. 273. Of. this Journal, 
ante, p. 93. 
Z Jahrb. f. wiss. Bot. (Pfefftr n. Strasburger), xxviii. (1895) pp. 359-486 (113 figs.). 
Cf. this Journal, 1895, p. 664. 
