AUTONOMOUS MOVEMENTS 



529 



remarkable autonomous movements which are perhaps of the nature of vari- 

 ation movements. In Stylidium adnatum (Gad, 1880) it is the gynostemium 

 which oscillates and which occasionally presses itself so vigorously against one 

 definite perianth leaf that tensions arise which in the long run may lead to a 

 sudden release of the co- 

 lumn from the leaf ; the 

 sudden backward curva- 

 ture thereby arising re- 

 sembles in its character 

 a reflex action. [Com- 

 pare HossENS, 1903.] 

 Among Orchidaceae os- 

 cillating movements 

 occur in Megadinium 

 falcatum{MoRREN,i842) 

 which are in this case 

 carried out by a narrow 

 basal part of the label- 

 lum, but of whose mode 

 of operation we know 

 nothing. Possibly it 

 may be a growth move- 

 ment, at least autono- 

 mous periodic movements are much more frequently due to growth than 

 to changes in turgidity. 



The whole cycle of growth under constant external conditions, i. e. the grand 

 period so called (Lecture XXIII), may with perfect correctness be regarded 

 as an autonomous movement. During that period the apex of the root or 

 the stem does not follow a perfectly straight course (circumnutation ; Darwin, 

 1881). Where such apices do appear to grow straight, looked at casually, the 

 microscope discloses inequalities in growth in certain longitudinal areas which 



,Fig. 



^ 162. Projection curve of 

 Phycnmyces nitens, after Fritzsche 

 200. 



(1899)- 



Fig. 163. Projection curve of 

 Zea wa?j, after Fritzsche (1899). 



Fig. 164. Yucca filamentosa, showing two axes of 

 inflorescence. 7, May 27, 1900, noon. //, May 28, 9.30 a.m. 

 ///, May 28, 2.30 p.m. From a pliotograph. Reduced. 



Fig. 165. Spirogyra princeps. 

 Positions taken up by a filament at 

 short intervals. After Hofmeister, 



1874. 



are sometimes regular, at other times follow no obvious rule (Fritzsche, 1899). 

 In Fig. 162 the movements of the conidiophore of Phycomyces are recorded, as 

 observed from above by means of the microscope. If the conidiophore grows 

 rectilineally its apex must always occupy the same position in the field of the 

 microscope, but in reality readings taken even after 7^ minutes show that it has 

 moved away considerably from that position. Similar records may be obtained 



