121 
the roots of shaded side develop.” Pfeffer suggested it was partly 
due to action of gravity and effect of contact with substratum, but 
chiefly to influence of light. 
The Lunulana (k,1, m,n, 0.) in the laboratory had well de- 
veloped gemmae cups ¥{ cm. in the long diameter, in which were 
gemmae in all stages of development, from four-celled up to de- 
tached gemmae of plates of several layers. These last were the 
characteristic fiddle shape and were .45 to .5 mm.in size. Several 
dozens of these tiny gemmae were planted in moist earth March 
2d. Three days later (March 5th), tiny rhizoids .1 mm. long had 
grown on surface touching the earth, the gemmae had grown to 
-97 by 0.5 mm. in length and breadth. 
Several were then /urned so that the upper side now became 
the side touching the earth, and allowed to grow four days, from 
March 5th to 9th. On examination long rhizoids 1 to 1.05 mm. 
in length had grown on what had been the upper surface, so we 
had the curious phenomenon of a gemmae with rhizoids on both 
surfaces. (p.a. q.b.) 
We next tried to find at what stage of development the ana- 
tomical characteristics become permanent, so that no change can 
be induced by change in position. 
Gemmae grown six days and having formed long rhizoids from 
I to 2 mm., on being turned, did not develop rhizoids on the dorsal 
surface, 
Full grown thallus, with tips turned, produced no result, so that 
the conclusion here is that, though dorsi-ventrality can be induced 
by light and other accessory assistants, yet, after a certain devel- 
opment of the thallus, and that early in its history, the dorsi-ven- 
trality becomes permanent and turning produces no change. 
Explanation of Pilate 297. 
Young twig of willow, buds still covered with scales, 3. 
. Cross section of a leaf from one of the buds, 90. 
Bud with leaves still folded, & 1%. 
. Section of outside leaf showing first indication of palisade tissue, circa 190. 
Bud unfolding showing leaves I, 2, 3, X 1%. 
Cross section of leaf 2, showing palisade tissue, circa 190. 
g. Cross section of leaf 3, showing palisade tissue, circa < 190. 
h. Leaf tied so under surface is exposed to light, >< 14. 
i. Cross section showing palisade tissue on both under and upper surfaces, circa 
xX 190. 
oP 
mem Bo 
