PRINCIPAL GROUPS OF PLANTS. 



27 



hairs of Cucurbita and Urtica and the hyphse or Rhizopus, etc. 

 This streaming movement in plants like Characeae, as pointed out 

 by Pfeffer (Physiology of Plants), has in most cases a definite 

 purpose. It is, in any case, always possible that the streaming 

 movement may be an accessory but unavoidable accompaniment 

 of some other form of vital activity. In Chara and Nitella the 



FIG. 13. Stonewort or Chara. At left showing the habit of the plant with minute 

 reproductive organs on the leaves. At right enlarged view of reproductive organs. A, 

 mature organs showing (a) antheridium, (S) oogonium surmounted at the top by a crown 

 of cells (c); b, stem of plant; /3', /3", whorl of leaves, some of which have been removed, as 

 at /3; B, a young antheridium (a), with young oogonium (SK), together with the adjoining 

 cells of the stem; the whorl of leaves not represented. A, after Wille; B, after Sachs. 



streaming endoplasm (inner layer of protoplasm) does not cover 

 more than 2 to 3 mm. per minute. The activity of the streaming 

 is influenced by sunlight, oxygen, acids, chloroforn^ etc. Two 

 kinds of protoplasmic streaming are recognized : ( i ) in which the 

 movement is confined to the layer enclosing the central vacuole, 

 that is known as " rotation," and (2) in which the streaming 

 follows more or less irregular paths up and down the strands of 

 protoplasm, crossing the latter, which is called " circulation." 



