158 



Minnesota Plant Life. 



nary Christmas-green variety, the same leaf which produces a 

 spore-case upon its upper surface is also depended upon by the 

 plant for leaf-green work, and the division of labor marks only 

 the higher types. 



The lowest in structure of all club-mosses is a New Zealand 

 form not more than an inch and a half or two inches in height 

 and typically unbranched. A single slender erect axis is pro- 

 duced, bearing foliage leaves near the base in a little rosette, while 

 above, the end of the stem develops as a cone with small spore- 

 forming leaves. Such a plant may be regarded as equivalent 

 to the cylindrical capsule of a 

 horned liverwort in which longi- 

 tudinal and transverse bands of 

 sterile cells have been developed 

 — something which was foreshad- 

 owed in certain horned liver- 

 worts — separating into chambers 

 the general layer of spore-moth- 

 er-cells surrounding the central 

 column. It is conjectured that 

 the sterile tissue in the ancestral 

 plants underneath each chamber 

 bulged out into a leaf-like expan- 

 sion and these leaves separated 

 from each other longitudinally. 

 Therefore the axis or stem of a fig. so. riatbranched ciub-moss. After 



Britton and Rrowii. 



club-moss is conceived to com- 

 pare best with the central cylinder of supporting tissue in a 

 horned liverwort capsule and not with the stalk of a moss cap- 

 sule. The leaves of the cone are conceived to compare with 

 sections of the capsular wall, each section bearing on its inner 

 surface its own portion of the spore-mother-cell tract. The root 

 is conceived to be a new structure, and outgrowth of the central 

 cylinder. The tip of the horned liverwort capsule is regarded as 

 equivalent to the tip of the cone in a club-moss. All these points 

 may be best understood by comparison with the simple New 

 Zealand club-moss in which abundant branching of the spore- 

 producing plant does not take place. 



As the spore-producing plant of the club-moss has acquired 

 new powers and new perfections of structure along vegetative 



