ILLUSTRATIONS OF ANISOTROPY. >JOl 



obliquely or horizontally, or even vertically downwards, as happens not rarely with 



W 



Fig. 394 (see the text). 



the lateral shoots of perennial shrubs and water-plants. Thus the first lateral 

 shoots of some plants with labiate flowers, as well as those of the Equisetineae 

 or Horsetails, penetrate vertically, into the earth 

 like primary roots, and certain lateral shoots of 

 the rhizome of Typha, Sparganium, some spe- 

 cies of Potamogeton, and many others behave 

 very similarly. It has also been already 

 mentioned that leaves may grow horizon- 

 tally, obliquely, or even erect; but there exist 

 also not a few foliar structures which grow ver- 

 tically downwards like primary roots, or, put 

 better, are negatively geotropic. Peculiarly 

 fine examples of these are found in the first 

 seed-leaves or cotyledons of some Monocoty- 

 ledons, e.g. the common Kitchen Onion (Fig. 

 395) : here, as shown in the figure, the primary 

 root together with the plumule is pushed out of the testa by the vigorous elongation 



Fig. 395. 



