EUROPE AND NORTH AMERICA, 



13 



appresscd to the stem, and these with the spongy cuticle of the 

 stem are far more effective than the roots for the transmission of 

 fluid, while the dense masses formed by the aggregation of stems 

 equally supersede the necessity for roots as fixing organs ; these, 

 therefore, being no longer needed, wither away and completely 

 disappear. 



The Stem. 



The young stem appears from tlie under side of the prothallium 

 by a change in the cell formation, some of the cells developing 

 downwards into hair-like radicles, while the upper cell elongates 

 and subdivides to form the young stemlet, some of the cells also 

 becoming free laterally to form the rudimentary leaves ; it is at 

 first transparent, but soon acquires chlorophyl granules, and a dif- 

 ferentiation into its cell layers is distinguishable at a very early 

 stage. 



When the young stem has attained a height of 5 mm. it throws 

 off at the sides simple flagellar branches, which arise laterally to 

 the uppermost leaves, and are at first crowded in the coma and 

 separate by elongation of the internodes. The branches come off 

 at every fourth leaf as an obtuse bud, on which, when it has 

 attained a height of three cells, leaves also form and division into 

 branches takes place. 



The growing point of the stem is conical, its terminal cell 

 apparently subdividing in five direction , and thus continually 

 elongating the stem ; by longitudinal division and transverse exten- 

 sion of newly formed cells, the terminal cone thickens from above 

 downward, and the base constantly forming anew attains the 

 diameter of the already completed stem. 



The trunk or perfectly developed stem consists of a simple 

 primary axis with numerous terminal shoots enclosing the central 

 terminal bud, and also of several secondary axes ; for each year a 

 lateral shoot is formed beneath the grc- -ing point, which is an 

 exact repetition of the original main stem, with which it keeps a 

 perfectly parallel advance in growth and development ; in fact, it 

 is nothing else but one of the fascicled lateral branches transformed 

 into an ascending axis, and this again repeats the process the 

 following season, so that we thus obtain not only the dense dicho- 

 tomous ramification, but the fastigiate surface so characteristic of a 

 cushion of Sphagnum plants. 



Professor Schimper in his great work described the stem as 



