THE BRYOPHYTA 



129 



may be found. Its cells are small, and in the older part 

 of the stem become very thick walled. The cortex is of 

 relatively great thickness, and made up of parenchyma, 

 the outer cells having thicker walls than the 'inner. 

 When young, the cortical cells contain chlorophyll. The 

 central cylinder consists of a very sharply defined 



Fia. 59. A, lower part of a Moss plant, bearing leaves and 

 rhizoids (r} } which grow up above the ground and become 

 secondary protonema (p). At b is an underground gemma 

 or bulbil. At k is a bud from which a new leafy stem will 

 grow. Magnified about 20. B, C, and D, successive stages 

 of germination of a spore of Funaria, producing primary 

 protonema. Magnified 200. (After Luerssen.) 



cylindrical strand of long, narrow, thin-walled cells, 

 destitute of chlorophyll. There is evidence that this 

 is a water-conducting tissue. In Funaria the central 

 strand is quite uniform throughout ; some of the larger 

 Mosses, however, have a more complicated arrangement, as 

 shown in Fig. 60, which represents the transverse section 

 of the central cylinder of Atrichum. 

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