294 



BOTANY 



PART I 



A peculiar mode of protoplasmic movement, wliich may 1)6 termed streaming, 

 occurs iu the non-septate mycelium of some Fungi. In it the whole mass of 

 protoj^lasm, with its included vacuoles, streams towards the end of the hypha, 

 only the limiting layer remaining at rest. After a longer or shorter interval a 

 similar streaming movement commences in the opposite direction (cf. Fig. 222). 

 Teknetz observed the same type of movement in the mycelium of Asco2}hanus 

 carncus, where the protoplasmic stream, with its vacuoles, makes its way throngli 

 the pores of the jierforated transverse septa. In this latter case it was established 

 that the direction of streaming was determined by local differences in the supply 

 of water. It is hardly doubtful that we have here to do with a normal vital 

 phenomenon (*^). 



Diatoms and Desmids exhibit quite a different class of movements. The 

 Diatoms glide along, usually in a line with their longitudinal axis, and change 

 the direction of their movements by oscillatory motions. From the manner in 

 which small particles in their neighbourhood are set in motion, it is concUnlcd 

 that there exists a current of ]irotoplasm, whicli bursts through the raphe ; this, 

 according to 0. Muller, is the cause of tlie mo\-ement ('"'). The cells of 



Desmidiaceae attach tliem- 





selves to the substratum by 

 mucilaginous excretions, and 

 effect their peculiar move- 

 ments by local fluctuations in 

 the mucilaginous layer. The 

 advancing movements of the 

 filamentous Oscillarieae and 

 Spirulinae take i)lace, accord- 

 ing to CoRRENs, in a muci- 

 laginous sheath, but their 

 mechanism is as little under- 

 stood as that of the slow 

 movements of Spirogyra. 



B. Curvatures 



/ 



Fia. 223. 



-Four-angled inisiii. I, straiglit ; II, curved 

 III, twisted ; I\', spirally wound. 



Tlie sorts of curva- 

 ture which ma}' take 

 place ill the organs of 

 attached plants are illus- 

 trated by Fig. 223. A 

 four-angled prism is of equal length along each of its angles. If it is 

 bent in one plane the angles of the concave side must become markedly 

 shorter than those of the convex side. An elongation of one side or 

 a shortening of the other side or simultaneous lengthening of one side 

 and shortening of the opposite side must lead to curvature. When in 

 this process of bending the column remains in one plane, it is spoken of 

 simply as a curvature. When, however, it passes out of the one plane 

 so that the bending follows a line oblique to the longitudinal axis it is 

 spirally wound (IV). Lastly, when the column remains as a whole 

 straight but its angles follow spiral lines, it is termed twisted. The 



