356 



Plant Physiology 



occurs throughout nearly all the phyla and classes of 

 organisms, and is of unquestioned importance. It is not 

 possible to consider the many interesting opinions regard- 



FIQ. 99. Pistil of squash : cross-section of style (A), with region of pollen- 

 tube penetration (a) ; portion of preceding, enlarged (B) ; longitud- 

 inal section (C) corresponding to the preceding ; cross-section of ovule 

 case (D) with region of pollen-tube penetration (a). 



