800 General Notes. | August, 
and of the outer ring, the divided bundle-ring afterwards closing 
up, leaving the arrangement the same as before. 
If, however, the branch is to be a frond, a connection is soon 
formed between the two sclerenchyma bands, dividing both bun- 
dles or rows of bundles between them. The beginning of this 
connecting band is seen in Fig. 1 B, a section at the base of the 
stipe just above the point of attachment. When this connection 
is completed the bundles all lie in one continuous, though dis- 
torted ring, the enclosed sclerenchyma occupying the place of 
pith. From this point upward the band of sclerenchyma which 
lies on the anterior side of the stipe gradually diminishes 
Fic. 1.—A, outline of a rhizome with base of stipe, 2-2; B, a horizontal section 
at point a; c, a bundle which divides; C, horizontal section at the point 4, The 
areas within the dotted lines are sclerenchyma, the others fibro-vascular bundles. 
A about one-half, B and C about twice natural size. 
in size and finally disappears, while the one on the opposite 
side becomes broader, its edges bend forward and the bundles 
bordering upon it divide and increase in number. During these 
changes the front of the stipe becomes nearly flat and the back 
more convex, as in Fig.1 C. Farther up all the sclerenchyma 
diminishes, and at the height of a few inches entirely disappears. 
The bundles, however, retain the same relative position and the 
pinne are given off right and left in the same manner as the 
branches of the stem. i 
In Fig. 1 B the bundle, c, divides and with part of the adjoin- 
ing sclerenchyma enters the bud between a and 4 Fig.1 A. In 
feeble plants this bud is suppressed and the branch at the left is 
uced to a bud, so that the stipe then seems to arise directly 
from the main axis.—A. A. Crozier, Ann Arbor, Mich. 
ATTEMPTED HYBRIDIZATION BETWEEN POND-SCUMS OF DIFFER- 
ENT GENERA.—In the latter part of May of this year, while ex- 
amining a dish of material containing duckweeds (Lemna poly- 
rhiza) and various fresh-water algæ collected in Southern Ne- 
aes ca, I came across a case of attempted hybridization between 
_ two pond-scums (Zygnemacez) of different genera, which is well 
_ worth recording. The plants concerned were Spirogyra majus- 
-~ cula and Mesocarpus scalaris, both rather common pond-scums of 
_ our ponds and ditches. The normal mode of conjugation in this 
_ Spirogyra is by means of short lateral branches which unite so as 
