134 Trans. Acad. Sci. of St. Louis. 



ulation of new soil when sown to clover and other legumin- 

 ous crops, though it must be added that the practical value 

 of this inoculation is thrown in considerable doubt by re- 

 cently made laboratory experimental tests. 



PROTOPLASM. 



Doubtless the most important of all discoveries in physiol- 

 ogy is that of protoplasm as the living working part of both 

 plants and animals, in the early phases of which von Mohl, 

 Robert Brown, Naegeli and Cohn played a prominent part. 

 Studies on this substance, its physical and chemical properties, 

 and its activity, have occupied many of the best chemical, 

 physical and biological investigators of the last half of the 

 century, and are destined to be the keystone of physiological 

 attainments in the century we are now entering upon. 



Though sex in the flowering plants was known long before 

 the century opened, to the extent that the co-operation of 

 stamen and pistil, and even the transfer of pollen from the 

 former to the latter, was recognized as necessary for the pro- 

 duction of fertile seed, — a fact, indeed, which Linnaeus in- 

 dicated and even amplified in his designation of the groups 

 which he called phanerogams and cryptogams, — it was not 

 until 1823 that Amici observed the growth of the pollen tube 

 to the ovule, and real fertilization, the union of protoplasmic 

 structures, was not demonstrated until the close of another 

 quarter of a century, when Hofmeister and Pringsheim at in- 

 tervals of a few years described it respectively for some of 

 the higher and lower cryptogams. 



The greatest advance in protoplasmic study was doubtless 

 made possible by Strasburger's introduction, in 1875, of 

 methods for fixing protoplasmic structures in certain desired 

 states of their transformations, by the use of killing and 

 hardening fluids, and the addition a few years later of dif- 

 ferential staining processes, as a result of which, largely 

 through his efforts and those of his pupils, the minutiae of 

 both cell division and cell union have been carried to a won- 

 derful detail, — perhaps the least expected result of which is 

 the closing discovery of the century of an unexplained double 

 fertilization in the case of the flowering plants, by which the 

 endosperm is formed as well as the embryo. 



