400 



EFFECT OF GRAVITY UPON GROWTH [Ch. XV 



wards." "Adventitious stolons grew directly downwards 

 towards the earth. This was most noteworthy when such 

 adventitious stolons arose from a reversed stem (with the apex 

 down) sticking in the sand ; under these circumstances the 

 stolon grew towards the apex. These descending stolons 

 showed occasionally twistings and curlings, such as are found 

 in tendrils. The newly arising sprouts [hydranths] behaved 

 in the reverse fashion from the stolons : they grew vertically 

 upwards" (Fig. 109). Subsequently, Loeb ('92, p. 8, '94) 



Ml/ 



Fig. 111. — A bit of regenerating stem ol Antennularia antennina placed in the water 

 obliquely, with the basal end downwards. The new hydranths (S) and stolons (W) 

 arise vertically. (From Loeb, '92.) 



Fig. 112. — A piece of the stem of Antennularia placed horizontally, and regenerating 

 stolons (r, r) downwards, and hydranths (6,c) upwards. (From Loeb, '94.) 



found another hydroid, Antennularia, which, whether the stem 

 was held inverted, oblique, or horizontal, sent out new stems, 

 which grew vertically upwards, and stolons, which grew verti- 

 cally downwards (Figs. 110, 111, 112). The growing stolon, 

 if moved out of its first position, will curve until it acquires 

 again its vertical direction. The geotropism of stolons has 

 been likewise carefully studied by Deibsch ('92). This 

 author found in a species of Sertularella that, although the 

 main stolons are not geotropic, the daughter (secondary) sto- 



