184 Macfarlane—Current Problems 
histological study. In plant physiology Linnzeus, Koelreuter 
and Sprengel had advanced inquiries into the fertilization, 
pollination and hybridization of plants to a degree that excites 
our highest admiration. Stephen Hales, Ingen-houss and de 
Saussure had grappled with problems of plant nutrition. 
Investigations into plant irritability had been largely confined 
to naked-eye studies of the leaves of M/zmosa, and the stamens 
of Cynara, Opuntia and Berberis. The important discovery 
by Corti in 1772, of protoplasmic circulation in Chara, was 
lost as a permanent contribution to science for half a century, 
through a false interpretation of the phenomena. 
The dawn of 1800 brought, therefore, only moderate hopes 
for the century now closing. The splendid results achieved, 
by all the workers who have lived through its years, have 
been due to unswerving faith in the motto “To the solid 
ground of nature trusts the mind that builds for aye.” 
It would be equally difficult and invidious were I to compare 
minutely the work and the workers of the century. Rather 
let me attempt to sketch hastily the great advances which 
have been made directly or indirectly owing to our increasing 
knowledge of the cell as the plant unit. In the first quarter 
of the century numerous investigations were directed to the 
cell wall as a growing anda mature structure. Each inves- 
tigator was thereby drawn more and more closely to the 
formative substance from which such walls proceeded, as 
furnishing the real basis for explanation of their growth, 
patterns and uses. In the second quarter of the century, 
therefore, the researches of Von Mohl, Schleiden and Robert 
Brown culminated in the recognition of the living cell as the 
plant unit. Botany thereby attained, for the first time in its 
history, to the dignity of an exact science. True, the organic 
units that make up each plant do not usually behave in the 
manner that chemists and physicists can predict for the 
simpler molecules with which they deal, but this, instead of 
