88 



RELATIONSHIPS OF SYMMETRY 



In lateral shoots, and in lateral members generally, there is a dorsi- 

 ventral construction which stands in a definite relationship to the chief 

 shoot, although as yet it is impossible to declare that this relationship is 

 anything else than a mere superficial one one depending upon the 

 conditions of space available. Fig. 42 is a diagram taken from an 

 individual instance of the branching of a shoot of Thuya occidentalis. 

 Each lateral shoot is at first dorsiventral and its first three to five 

 branchings appear only on the side turned towards the mother-shoot, 



FIG. 44. 



FIG. 44. Halopteris Clicina. Apex ol a long shoot. 

 Magnified. 



FIG. 45. 



FIG. 45. Plocamium coccineuni. The lateral branches always stand upon one side, the growth is sympodial. 

 At HI, Ai>, ff$, are anchoring discs by means of which the plant is attached to another alga (Z). Magnified. 



the later ones stand alternately on the two angles, and we cannot suppose 

 that this unilateral position at the beginning of the shoot is the result 

 of an influence either of gravity or of light. The same thing is found in 

 many Algae. Compare, for example, Fig. 44, representing Halopteris 

 filicina l , which has the lowermost lateral branches of each primary branch 

 turned towards the chief axis, the following ones alternating ; the same 

 is found in Euptilota (shown in Fig. 46) where the outer side has preference. 



1 Out of 44 examples of Stypocaulon examined by Geyler the first branch of the second order 

 upon branches of the first order was directed outwards in 8, directed inwards in 36. There was here 

 then overwhelming preference for the inner side, but no constancy. See Geyler, Zur Kenntniss der 

 Sphacelarieen, in Pringsh. Jahrb. iv. See also Berthold, Beitr. zur Morphologic und Physiologie der 

 Meeresalgen, in Pringsh. Jahrb. xiii. 



