366 BOTANICAL GAZETTE [MAY 
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. RoTHERT, W.: Die Streitfrage iiber die Funktion der Wurzelspitze, 
os 79: 179. 1894. 
22. ROTHERT, W.: Ueber Heliotropismus, Cohn’s Beit. z. Biol. der Pflan- 
zen. 1895. 
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ter sich aufwarts krummender Sprosse, Arb. d. Bot. Inst. z. Wiirzburg 1: 193- 
1872. 
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Bot. Inst. z. Wiirzburg 1: 385. 1873. 
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1865. : 
27. Sacus: Text-book of Botany, 2 Eng. ed. 853. 1882. 
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Q 
EXPLANATION OF PLATE XXVIII. 
C. Median longitudinal — of motor zone of root of Zea geotropically 
excited and curved through 105°. The epidermal cells of the convex side — 
have collapsed. A few root us are to be seen on the basal end of the 
motor zone. After a photomicrograph. 
S. Median longitudinal section of motor zone of Zea geotropically excited 
and curved through 60°. The epidermal cells of both sides are normally 
turgid, and both exhibit root hairs. The differences between the contours 
of the cortical cells of the convex and concave sides are not so apparent 
dinal section of motor zone of straight root. Aes 
wi! of a median longitudinal séction of motor sons oh 
a p, epidermis; 7f, cortical parenchyma; gés, endodermis; lzb, 
_fibro-vascular bundle; %, wood cells; g, vessels. The cells of the half — 
toward the nadir are smaller than. those of the side toward the zenith; the — 
—* of the upper half are stretched ily, while those of the vasa 
seamed 8 folded. contents are much denser than of the WEP 
