CONOVER ON ASPARAGUS PLUMOSUS. 65 



illumination, light is the directive agent. The vigorously growing tip 

 seems to be more responsive to light than to gravitation, hence the tip 

 curves from the vertical line in which the tensions from negative 

 geotropism is at a minimum to a jxisition where the eipiilibrium between 

 the two agents is established. When diageotropism and heliotropism 

 work in the same direction a permanent position is the result. 



In all the foregoing experiments, observations were made on the pri- 

 mary and secondary branches and cladophylls. Under changing posi- 

 tions, they invariably sought the horizontal plane. 



In the younger stage heliotropic response precedes diageotropic in 

 branches as well as in primary stem, i. e., the branches place themselves 

 with reference to the light before reaching the horizontal plane, but 

 as stated before, the growing, tips of older branches seek the horizontal, 

 less influenced by the light. 



Lines of ink drawn along the stem, together with the arrangement 

 of the branches determined the fact that there is no permanent morpho- 

 logical upper and lower side. The lighted side of the young shoot be- 

 comes the concave and lower side of the dorsi-ventral portion. The 

 upi)er side of the branch is dependent on the side and place from which 

 it springs from the main stem. AVith changed positions these first 

 determined upper sides do not necessarily remain constant as shown by 

 the experiments. 



On questions of nutation, circumnutation and twining, fewer ob- 

 servations have been made, but a sufficient number of facts have been 

 ascertained which lead at least to temporary conclusions. 



Young shoots begin to nutate soon after their appearance through 

 ground and as they grow older their growing tips pass through larger 

 areas until they may be said to circumnutate. Near the time when the 

 stem is beginning to make the diageotropic curve, the curves described 

 by the terminal portion become more complicated and what appears 

 like a periodic wilting and recovering occurs. Later the circuit con- 

 sists of series of compound curves or loops not unlike those made in 

 Indian club exercises. The point of one stem rose and fell three times 

 before it reached the position from which it started two hours before. 

 ^^■hile the stem appears to have lost all turgescence during the wilting- 

 period, it does not become limp but begins to rise in a short time. 



Until a certain stage in the stem's development has been reached, 

 regular twining about strings does not occur but when twining does 

 begin it continues at regular intervals clockwise or counterclockwise 

 until vigorous growth ceases when the last three or four inches become, 

 like the shorter stems, a dorsi-ventral member. 



Not only do primary stems nutate but the younger branches rise and 

 fall, often simultaneously, while tracing their curves. This phenomenon 

 was seen to occur on different plants near noon of several different days 

 also late in the afternoon. It took place when the plant stood in a 

 north window in winter, as well as in a well lighted greenhouse in mid- 

 summer, which leads me to think it is a fixed characteristic of the plant 

 in its rapidly groAving stages. 



None of the stems thus far observed have been sensitive to contact, 

 consequently the twining must be due to circumnutating stems striking 

 against a resisting cord which becomes the axis of rotation as long as 

 circumnutation continues. 

 9 



