THE HAMILTON ASSOCIATION. 93 
One important difference exists, however, between the macrospore 
and the embryo-sac. The former becomes detached from the 
sporophyte which produced it, while the latter always remains 
in conjunction with the sporophyte producing it. The micro- 
svore of the heterosporous plants is the equivalent of the pollen 
grain in the flowering plant. 
Previous to fertilization in the flowering plants important 
changes take place within both the embryo-sae and the pollen 
grain, resulting in the reproduction of structures, which must be 
considered gametophytes. The reproductive organs, if they can 
be called such, found in connection with these gametophytes are 
somewhat rudimentary. The germ cell is not contained in an 
Archegonium, as: in the preceding plants, while structures re- 
sembline the autherozoids have been found in only one or two 
cases in the Phanerogams, and that in plants very closely allied 
to the heterosporous pteridophytes. 
A great deal of work remains to be done before it can be 
authoritatively stated that evolution among plants has taken 
place along any one line. Much has been done in this field in 
recent years. Many readjustments have been made as new light 
has been thrown on points that were somewhat obseure. <Ad- 
ditional workers are constantly taking their place in the ranks 
of the great army of patient and painstaking investigators, so 
that while the past has been productive of good results, the future 
holds out promise of still greater achievement. 
