2o6 MONOSTROMA, ULVA, AND NITELLA less. 



towards the distal end the internodes become rapidly shorter 

 and the whorls consequently closer together, until, at the 

 actual distal end, a whorl is found the leaves of which, in- 

 stead of spreading outwards like the rest, are curled upwards 

 so that their points are in contact. In this way is formed 

 the terminal bud [term, bud), by which the uninjured stem 

 is always terminated distally. 



The angle between the stem and a leaf, above (distal to) 

 the attachment of the latter, is called the axil of the leaf. 

 There is frequently found springing from the axil of one of 

 the leaves in a whorl a branch or shoot (br) which repeats 

 the structure of the main stem, i.e. consists of an axis from 

 which spring whorls of leaves, the whole ending in a ter- 

 minal bud. The axis or stem of a shoot is called a second- 

 ary axis, the main stem of the plant being the primary axis. 

 It is important to notice that both primary and secondary 

 axes always end in terminal buds, and thus differ from the 

 leaves which have pointed extremities. 



The rhizoids or root-filaments {rh) arise, like the leaves 

 and branches, exclusively from nodes. 



In the autumn the more distal leaves present a peculiar 

 appearance, owing to the development on them of the ^i,''^««^^ 

 or sexual reproductive organs (Fig. 44, b and g) : of these 

 the spermaries (antheridia) look very like minute oranges, 

 being globular structures {spy) of a bright orange colour : 

 the ovaries (oogonia) are flask-shaped bodies {pvy) of a 

 yellowish brown colour when immature, but turning black 

 after the fertilization of the ova. 



Examined under the microscope each internode is found 

 to consist of a single gigantic cell (f, int. nd^) often as much 

 as 3 or 4 cm. long in the older parts of the plant. A node 

 on the other hand is composed of a transverse pl^te of small 



