ADDKESS. lxwii 



Leaving, however, these and many other general questions regarding the 

 origin of the lowest forms of animal and vegetable life, let us now turn 

 our attention to the mode of development of a new heing in those possessing 

 more obvious and known germs. The general nature of the formative pro- 

 cess, in all instances where fertilized germs are produced, will be best un- 

 derstood by a short sketch of the phenomena ascertained to occur in different 

 kinds of plants. 



In the higher or Phanerogamic plants it is generally well known that tho 

 combination of two parts of the flower is necessary to the production of a seed 

 containing the embryo or young plant. Beginning with the discovery of the 

 pollen-tubes by Amici in 1823, the careful and minute investigations of a long 

 liue of illustrious vegetable physiologists have broiight to light the details of 

 the process by which fertilization is effected, and have shown, in fact, how the 

 minute tube developed from the inner membrane of the pollen-granule, as 

 soon as it falls upon the stigmatic tissue of the seed-bearing plant, insinuates 

 itself by a rapid process of development between the cells of the style, and 

 reaches at last the ovide, in the interior of which is the embryo-sac ; how, 

 having passed into the micropyle or orifice of the ovule, it makes its way 

 to the embryo-sac ; how a minute portion of the fertilizing substance of 

 the fovilla transudes from the pollen-tube into the cavity of the embryo-sac, 

 in which by this time a certain portion of the protoplasm has become differ- 

 entiated into the germinal vesicle — thereby stimulating it to further growth 

 and development, the earliest phenomena of which manifest themselves by 

 the formation of an investing cell-wall, and by the occurrence of cell-division 

 which results in the formation of the embryo or plantule of the seed. 



Thus it appears that the essential part of the process of production in Pha- 

 nerogamic plants is the formation in the parent plant of cells of two different 

 kinds, which by themselves have little or no independent power of further 

 growth, but which, by their union, give rise to a product in which the power 

 of development is raised to the highest degree. 



By further researches it is now known that the same law prevails in all tho 

 remaining members of the vegetable kingdom, with the exception only of tho 

 very simplest forms *. 



In viewing the reproductive process in the series of Cryptogamic plants, 

 two facts at once strike us as remarkable in the modifications which are 

 observed to accompany the formation of a productive germ, viz. : — first, that 

 the difference between the two productive elements becomes more prominent, 

 or as it were more higbly specialized, in the Cryptogamic than in the Pha- 

 nerogamic plants ; and second, that in the simpler and lower forms this differ- 

 ence gradually disappears till it is lost in complete uniformity of the pro- 

 ductive elements. 



* It will be observed that I leave entirely out of view the whole subject of the multipli- 

 cation of plants by budding or simple division. 



