THE POLLEN GRAIN — THE EMBRYO. 411 



holic solutions of iodine, which would immediately 

 kill such ; and he pronounces the contents of these 

 tubes as nothing more than a " solution of gum, and 

 small crescent-formed bodies, which are starch." 



lie doubted the wisdom of tracing the analogy 

 between the animal and vegetable kingdoms, and 

 denied even the sexuality of plants as generally 

 understood • that if the pollen-tube be followed to 

 the ovule, it will be found that generally only one 

 reaches the embryo sac, and, forcing and indenting 

 that part which it comes against, it forms the " cylin- 

 drical bay which constitutes the embryo in the first 

 stage of its development ; " and that it consists only 

 of a parenchymatic cell. Thus, on all sides except 

 one end, the embryo has a double membrane, having 

 that of the indented sac, and that of the pollen- 

 tube. Thus the latter becomes the embryo. This 

 he has proved, because he has been able to separate 

 the tube from the sac after it had considerably ad- 

 vanced in development. He stated, even while the 

 contents of the pollen grains and the tubes at first 

 are simple starch, that they may be changed chem- 

 ically in the inter-cellular passage, or they may not. 

 Yet from this starch cells are formed at the ter- 

 minus of the tube, which eventually become the 

 parenchyma of the embryo. He found additional 

 proof in the fact that where there was more than 

 one embryo in a seed, there was a corresponding 

 number of pollen-tubes present. Considered in this 



