Ril 
; 
a 
1904] CURRENT LITERATURE 153 
The promised second part dealing with the vegetation will probably be of greater 
interest —P. OLssoN-SEFFER. 
Wiesner describes’? casting of leaves in summer due to deficient light and 
to consequent interference with photosynthesis, which is distinct from a similar 
effect of drouth and heat and not continuous with the autumn defoliation. The 
loss amounts to 8-30 per cent. of the foliage in sensitive trees. It begins, in those 
trees which complete their leaf formation in spring, when the midday sun has 
reached the same elevation at which foliation was completed, whereas it is almost 
imperceptible in trees whose foliation extends into the summer.—C. R. B 
Brarp?? has discussed “the track of heredity” in plants and animals, chiefly 
the latter. A‘ luminous statement in reference to plants is as follows: “In the 
embryo-sac of Pinus, which is the gametophyte, there are only four germ-cells. 
In the corresponding structure in flowering plants there are perhaps three, or 
at most six; while, as is well known, the male gametophyte of a flowering plant 
is represented by one or two vegetative cells and one or two germ-cells.”” ‘This 
may be clear to a zoologist, but its interpretation is beyond the powers of the plant ~ 
morphologist—J. M. C 
BLAKESLEE?" has made preliminary announcement of his results in a study 
of the methods of reproduction in Mucorineae. It seems that zygospore produc- 
tion in this group “is conditioned by the inherent nature of the individual species 
and only secondarily or not at all by external factors.” Two methods of zygo- 
spore formation are recognized, and upon this basis Mucorineae may be divided 
into two groups designated as “homothallic” and “‘heterothallic,” the terms 
corresponding to “monoecious” and “dioecious” among higher forms. The 
general conclusions are that the formation of zygospores is a sexual process, 
that the mycelium of a homothallic species is bisexual, that the mycelium of a 
heterothallic species is unisexual, and that among the heterothallic species certain 
ones have a distinct differentiation of sex. It is interesting to note that in conju- 
gation the swollen portions (‘‘progametes”’) from which the gametes are cut off 
do not “‘grow toward each other,” as commonly stated, but arise as a result of 
Me ies of contact between hyphae, and are from the outset adherent.— 
Masters”? has published a synopsis of the genus Pinus, the purpose of which 
he states is “to add to our knowledge of the species and to facilitate their deter- 
ne 
WL 7 oe Uber Laubfall pies ase des absoluten Lichtgenusses 
ieseaien, Ber. Deutsch. Bot. Gese 2:64-72. 1904. 
7° BEARD, J., The track of heredity in oi and animals. Trans. and Proc. 
Bot. Soc. Edinburg 22: 126-155. figs. 3. 190 
: *" BLAKESLEE, ALBERT FRANCIS, ae formation a sexual process. Science 
N. S. 19:864-866. 190 
_ 72 MASTERs, ERE T..A it ie view of the genus Pinus. Jour. Linn. Soc. 
t. 35: 560-659. pis. 20-23. 
