i 
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; 
1907] HIBBARD—FORMATION OF MECHANICAL TISSUE 381 
Ricinus communis 
It may be said by way of summary that twenty-five out of the 
thirty-four Ricinus plants under tension in this series show a greater 
development of mechanical tissue in both the main and lateral roots 
than in the control plants. Sections of the primary roots show con- 
siderable differences, while the secondary roots show some but not so 
great differences in favor of the tension plants. 
Helianthus annuus 
The plants for comparison were chosen from the series of experi- 
ments in the open field during the latter part of the summer. The 
evidence obtained from observations upon the main roots of twelve 
seedlings of Helianthus annuus shows that nine reacted to tension 
by an increased development of mechanical tissue, while all the lateral 
roots examined showed a greater development of mechanical tissue 
in the tension plants. 
IV. Summ 
In the foregoing work, of the five stems tested for the increase of 
mechanical tissue under the influence of longitudinal pull, only that 
of Vinca showed a response, and in this the increase was not great. 
Pull in the direction of the longitudinal axis of the plant called 
forth a small increase of mechanical tissue in the main and lateral 
roots of Helianthus annuus and Ricinus communis. 
Compression tension brought small increases of mechanical tissue 
in the stems of Fuchsia, Vinca, and Helianthus. By the same method 
Coleus gave no response. 
The investigation, the results of which are here recorded, was 
carried out under the direction of Professor F. C. NEwcoMBE, to 
whom I wish to express my grateful thanks for kindly encouragement 
and helpful suggestions. 
University, oF MICHIGAN, 
ANN ARBOR, MICH. 
LITERATURE CITED 
ee O. M., :04, Der Einfluss von Zug auf die Ausbildung von Festungsgewebe. 
Jahrb. Wiss. Bot. 39: 305. 
Boopte, L. A., :02, On Hignification of phloem in Helianthus annuus. Annals 
of Botany 16: 180 
Dennert, E., ’87, Anatomische Metamorphose der Bliithenstandaxen. Bot... 
Hefte, Forschungen aus dem Bot. Garten zu Marburg, Heft 2: 128-217. 
Abstract in Bot. Jahresb. 18877:647. 
