3o ELEVENTH REPORT. 



One sample contained Sinapis arvensis (white mustard). 



One sample contained Verbena hastata (l)liie vervain). 



One sample contained Chaetochloa Italica (Hungarian grass). 



One sample contained Carduus lanceolata (bull thistle). 



One sample contained Arenaria serpyllifolia (a chickweed). 



One sample contained Amaranthus graecizans (a tumble weed). 



One sample contained Solarium rostratiun (beaked nightshade). 



One sample contained Lepidium campestre (a common peppergrass). 



One sample contained Silene vulgaris (bladder campion). 



East Lansing. April 1. 1909. 



THE EFFECT OF LONGITl DIXAL C0:\IPRE8SI0X UPON THE PRO- 

 DUCTION OF MECHANICAL TISSUE IN STEMS. 



[Alxstract.] 

 L. H. Pennington. 



This work was undertaken to determine whether a pressure exerted in the 

 direction of the long axis of a growing stem may act as a stimulus to cause 

 the plant to produce more or stronger mechanical tissue in the part under 

 compression. 



For each experiment a series of plants of the same age and of uniform size 

 were selected. The height and at least two diameters of each plant were 

 measured, one diameter of the part to l^e compressed and the other of the 

 part a short distance above the comj^ressed portion. At a suitable distance 

 from the ground, looj^s were tied around each stem, which was prt)tected from 

 injury by pieces of soft cloth. Each plant was then securely fastened in a 

 ]ierpendicular position by stakes to prevent Ijending or swaying, and weights 

 were suspeiuled from the loops upon half of the plants while the other half 

 were left without weights to serve as controls. At the conclusion of the 

 experiment the plants were measured as at. the beginning of the experiment 

 and each stem was te.sted to determine its resistance to bending and to 

 crushing. From suitably ])repared and stained cross sections of the stems, 

 measurements were made to determine the relative amount of mechanical 

 tissue. 



Both woody and herbaceous plants were used. The woody j^lants were 

 sprouts and seedlings of the common locust, Rohinia Pseudo- Acacia, sprouts 

 of the Aspen. Populus tremuloides. and ])oth young and one-year-old sprouts 

 of Sumach. Rhus glabra. The herbaceous jilants were the common Sun- 

 flower, Helianthus annuus, the Castor-oil Plant, Ricinus communis, and 

 the broad bean, Vicia faba. In the ease of woody shoots, the experiments 

 were begun in the spring before growth began and continued until autumn, 

 additional weights being added as the stems became able to bear them. In 

 some series of herl:)aceous stems, veiy young jilants were used, in others older 

 plants were used; some series were kept under compression for a short time, 

 ten to fifteen flays, others for longer jieriods. 



In no case however, did the average of a series of experimental plants show 

 a gain in strength or in mechanical tissue over a like series of control plants. 



Ann Arbor, A])ril 12, 19i 



