The first of the modern schools was formed when Ohara Unshin broke from the Ikenobo school in the late 19th century.  The Ohara School generally uses moribana (piled-up flowers) in a shallow, flat container.
The school was started at a time when Western culture was heavily influential in Japan and the moribana style made good use of Western plants.
But it was still a formal style.  Influence from the artistic movements of the early 20th century led to the development of jiyuka (free- style) arrangement. Despite all the changes, ikebana was still only for the upper class.
In  the 1930's  and  then  more  so  in  the post-war  period,  interest  in  ikebana
became  much  more  widespread.  Ikebana schools opened, which attracted people of all social classes.
During the occupation, many wives of US servicemen took up the art and later helped it spread abroad.
Led by Sofu Teshigahara, founder in 1927 of the Sogetsu school, zen-eibana
or avant-garde ikebana introduced all kinds of new materials, such as plastic, plaster, steel, paper, etc...    
For more info on Sogetsu school, please click on the green leaf……………..