THE STATOCYSTS OF STEMS 



007 



The statoliths of stems are generally highly mobile, a deflection of 

 the organ from the vertical of 10 or 11 usually producing a measur- 

 able displacement of the falling starch-grains (Fig. 252). 



In respect of their living contents, the statocysts of stems resemble 

 the corresponding cells of roots. The cytoplasm forms a uniformly thin 

 peripheral layer, and is hyaline 

 and apparently very liquid. The 

 sap-cavity may be traversed by 

 protoplasmic filaments. The 

 nucleus is usually arranged with- 

 out reference to any rule, but 

 sometimes adheres to the upper 

 transverse wall. The walls re- 

 semble those of ordinary par- 

 enchymatous elements. 



A typical starch-sheath 

 containing normal statoliths 

 only occurs in those regions of 

 the stem that are still engaged 

 in longitudinal growth, and that 

 hence are capable of executing 

 geotropic [or other] curvatures. 

 In fur ' developed and there- 

 fore no longer geotropically 

 responsive parts of the stem, 

 the layer in question is usually 

 empty, its starch having been 

 dissolved and employed in the 

 nutrition of the adjacent grow- 

 ing tissues ; this nutritive ac- 

 tivity of the starch-sheath must, 

 however, be regarded as a strictly 

 subsidiary function. When the cells of the sheath are about to lose 

 their sensory capacity, the impending dissolution of the starch is often 

 preceded by a scattering of these bodies. 



According to the author's observations, the geotropically sensitive 

 nodes [nodal pulvini] which occur in most Kubiaceae, Cakyophyllaceae, 

 Polygonaceae, Geraniaceae and Commelynaceae invariably contain a 

 typical starch-sheath. A similar layer has also been found by Nemec 

 in the foliar pulvini of certain Leguminosae (Phaseolus, Lupinus), the 

 nyctitropic movements of which are, according to A. Fischer, affected 

 by gravitational stimuli as well as by variations of illumination. 

 Mention has already been made of the " starch-crescents " which 



Fio. 252. 



Small portion of a radial L.S. through a node of Trades- 

 cantia virginica, which has been displaced from the 

 vertical (indicated by the arrow) for some time. Note 

 the position of the statoliths. 



