370 EVENINGS AT THE MICROSCOPE 



the outline and plan of this compound organism. Along 

 the smooth and lubricous surface of the olive weed runs 

 a fine thread of a pellucid white appearance, so firmly 

 adherent that if you attempt to remove it with a needle's 

 point you find that you only tear either the leaf or the 

 thread. The course is generally in a straight line, but 

 does not ordinarily pursue the same direction far, com- 

 monly turning off with an abrupt angle at intervals of 

 about an inch, and thus meandering in a zigzag fashion, 

 very irregularly, branching frequently, and uniting with 

 a thread already formed, when the creeping one has to 

 cross it. 



Thus the basal network is formed; but meanwhile, 

 from every angle, and often from intermediate points, a 

 free erect thread has shot up like the stem of a tiny plant 

 to the height of an inch, rarely more; not, however, 

 straight, but with frequent zigzag angles, whence the name 

 geniculata, or "kneed." At every angle a slender branch 

 is sent forth, pursuing the same direction as that of the 

 joint from the summit of which it issued, and terminating 

 in a tiny knob. In the angles of some of these branchlets 

 are seated oblong vesicles, twice or thrice as large as the 

 terminal knobs. And this is pretty well all that we can 

 make out with the naked eye. 



Cutting carefully off with scissors a narrow strip of the 

 leaf, I drop it into the parallel- sided cell of glass half filled 

 with sea- water, and examine it first with a low power, 

 and afterward with a higher. We now see that the creep- 

 ing thread is a tube of horny substance, flattened on its 

 under side, and that the erect stems and their branches are 

 similar tubes, whose cavities are in free communication 

 with that of the creeping root. The wall is thin, and per- 



