Index. 
Vll 
B. LIST OF ILLUSTRATIONS. 
a . Plates. 
I. 
II. 
Ill, IV. 
V, VI. 
VII, VIII. 
IX. 
X. 
XI. 
XII. 
XIII. 
Porphyra (Grubb). 
Crystal Cyst Formation (Samuels). 
Sphaerocarpos (Rickett). 
Crown Gall (Robinson and Walkden). 
Flower of Dipsaceae (Szabo). 
Fossil Plant 1 Impressions ’ (Walton). 
Golden Oak (Williamson). 
Oenothera (Gates). 
Chromosomes of Oenothera (Gates). 
Effect of Boron on Plants (Warington). 
b . Figures. 
i, 2. Potamogeton sp. (broad-leaved, submerged form), i a, transverse section of inner 
part of apical bud. i B, transverse section of squamule marked with arrow in 
i A. i C and D, changes in shoot apex as tip is approached. 2 a-h, series of 
transverse sections from below upwards through three successive young leaves and 
growing-point of another bud (Arber) ........ 
3. Potamogeton natans, L. 3 a-e, series of transverse sections from below upwards 
through apical bud including two successive leaves and the squamules within 
them. 3 f and G show further changes in the development of the second leaf and 
the squamules. 3 F, from a broken section, somewhat reconstructed as regards 
tig. s. x and sq. a on right (Arber). 
4. Cymodocea isoetifolia, Asch. 4 A, B, C, E, series of transverse sections passing 
upwards from below through an axillary bud (whose further history has not 
been followed), and its prophyll borne laterally on an axis. 4 A and B show 
detachment of margins of prophyll. 4 C, complete detachment of lateral bud, 
from which the prophyll is at this level only partly free. 4 D, region to left of 
arrow in 4 C. 4 E, stage at which bud, squamules, prophyll, and parent axis 
have become free from one another (Arber) ....... 
5. Tryglochin maritima, L. 5 a, b, c, F, G, h, serial transverse sections from below 
upwards through young leaf, and the apical bud with younger leaves, which it 
encloses. 5 A, margin of leaf-sheath of l. x free on left side, but, owing to slight 
obliquity of section, cut at a lower level on right-hand side, and there fused with 
axis. 5 c, section at a slightly higher level, showing three sets of squamules, ex¬ 
ternal respectively to /. 2 , and /. 3 . 5 b shows the three squamules marked with 
a cross in 5 c, cut at a slightly lower level. 5 D, detached squamule marked with 
arrow to left of 5 C. 5 e, attached squamule marked with arrow to right of 5 C. 
5 F, G, H, sections through l. x and /. 2 at higher levels, to show development up 
to point of separation of ligular sheath and petiole of l. x (Arber) . 
1. The Conduction of Geotropic Excitation in Roots (Snow) . 
2 > 3 - >> y> 
4 * >> >> 5 > » . 
Stages of Development of frond (Waight) . .. 
1,2. 1. The apical sporangial region of a hyphal filament, showing the dense cytoplasm 
and spherical nuclei. 2. The middle portion of a hypha, showing two kinds of 
cytoplasmic strands and elongated nuclei. Most of the nuclear divisions occur in 
this region (Smith). 
3-5. 3. The base of a hypha, where the cytoplasm is much less dense. The nuclei are 
long and pointed at the ends. 4. A typical resting nucleus, spherical in shape, 
with pronounced linin threads and granules on the membrane. 5. An elongated 
form showing chromatin on the membrane (Smith) ...... 
6-12. 6. The first stage in the amitotic elongation of the chromoblast. 7. The second 
stage in the division. 8. The third stage. The chromoblast is constricted in 
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