Minnesota Plant Life. 135 



warping" of a plank, yet it serves a purpose in assisting the spores 

 to escape from the capsule. By means of the writhing motion 

 of these curious cells the spores are separated from each other 

 and are not permitted, in the economy of the plant, to fall in 

 an inert mass at one place. 



In its stalked capsule and in the development of these claters, 

 as the writhing cells are called, the cone-headed liverwort marks 

 an advance in its spore-producing generation over the mud-flat 

 liverwort ; for in that plant and its immediate allies the capsule 

 had no stalk nor were there any elaters mingled with the spores. 

 In the sexual generation of the cone-headed liverworts there 

 exist a variety of other improvements in structure over the 

 mud-flat species. The plant-body is much larger and more 

 robust, the air-chambers are more regularly disposed, giving, 

 as they shine through the skin of the plant, the diamond-shaped 

 marking to the surface. Each air chamber has a central dome 

 of colorless cells and in the middle of each dome there is an 

 opening or air-pore which serves as an aperture through which 

 an interchange of gases may take place between the starch- 

 making cells that line the chamber — where they are best dis- 

 played on its floor — and the outer air. 



Another improvement is observed in the production of spe- 

 cial branches with cone-shaped heads for the development of the 

 egg-producing organs. In the mud-flat liverwort neither these 

 nor the spermaries were formed on branches differing in any 

 important respect from the ordinary branches. Therefore, in 

 the mud-flat liverwort when the egg had developed into an 

 embryo the spore-producing capsule found itself imbedded in 

 the general tissues of the sexual plant, and was not able to dis- 

 tribute its spores until the stem had decayed. But in the cone- 

 headed liverwort with its special branches, the egg-producing 

 organs, when their eggs had been matured, fecundated and de- 

 veloped into embryos, were all lifted up into the air a couple of 

 inches or so by the elongation of the slender special stem. By 

 this means the ring of capsules on the under side of the cone- 

 head gain an opportunity to scatter their spores over a much 

 wider circle, thus adding to their chances of germination and 

 growth. In order to eject the spores the tiny green stalk of 

 the capsular plant elongates a little just before the capsule opens, 



