360 
is a reducing division in the Weismann sense. The process of re- 
duction in Lz/ium is now regarded by Mottier and Strasburger as 
follows: the double-spireme of the pollen-mother-cell segments 
into 12 chromosomes; each double chromosome bends to form 
a U; each chromosome then splits through the plane of longi- 
tudinal division during the first mitosis and the daughter-chromo- 
somes have the form of a V. During the second mitosis each V 
divides transversely at the angle, a reducing division in the Weis- 
mann sense thus taking place. Each of the original double 
chromosomes has the value of a tetrad, the segregation of the 
chromatin into the compact solid tetrad being the only step lack- 
ing to make the process correspond wfth Haecker’s description 
tion of tetrad formation in certain copepods. Tetrads agreeing 
exactly with those of animal reproductive cells were observed and 
pictured by Osterhout in the case of Lguisetum, but it is to be re- 
gretted that he offers no observations regarding their mode of ori- 
gin or their fate. | 
In many cases the conclusions drawn from the observations 
brought together in this important collection are not wholly satis- 
factory. For example, the general denial of the existence of a 
centrosome in the higher plants cannot be accepted upon the 
mere statement. Evidence to the contrary is furnished by some 
of the figures, as in the case of Figure 63, Plate V, where a struc- 
ture is pictured at the lower pole of a cell of Hel/eborus, which 
agrees very closely with the centrosomes described by Guignard. 
: Gary N. Carkins. 
A Flora of Northwest America. Containing brief descriptions of all 
the known indigenous and naturalized plants, growing without 
cultivation, north of California, west of Utah and south of 
British Columbia. By Thomas Howell. Vol. 1, Phanero- 
gamae, Fasicle 1, Ranunculaceae to Rhamnaceae. Price 50 
cents. Portland, Oregon. March 15, 1897. | 
One of the most interesting and welcome contributions to 
Botany that has recently appeared is, without doubt, the first fas- 
cicle of Howell’s “ Flora of Northwest America.” 
The author’s remark in his preface, that all the territory of the 
United States of America, south of the British boundary, except 
Oregon, Washington and Idaho, is supplied with “ Floras,” is 
