-1-^4 Journal of Applied Microscopy 



Laboratory Outlines for the Elementary Study of Plant 



Structures and Functions from the Standpoint 



of Evolution. 



XXII. Ulothrix zoiiata (W. & M.) Ktz. Order, Confervales. Family, 

 Ulothrichaceae. 



This Ulothrix is a small, unbranched, filamentous, green alga which usually 

 grows in running water, attached to sticks or stones. It may be found in slow- 

 flowing streams, in watering troughs, or in fountains. Collect the material and 

 place it in a shallow dish in about two inches of water, and in a day or two, 

 after the water has evaporated somewhat, large non-sexual zoospores and sexual 

 gametes will probably be forming. Study the fresh material and preserve some 

 for further use. 



1. Mount some of the filaments containing the basal cells (holdfasts) and 

 study under low power. Draw. 



2. Under high power draw the holdfast, the terminal cell, and two or three 

 of the central cells ; showing the wall, the chloroplast, and the nucleus. Describe 

 these parts. 



3. Non-sexual zoospores. Examine a filament in which the cells are form- 

 ing either one, two, or four zoospores each. Observe how they escape by a 

 lateral opening in the cell-wall. Draw and describe. These spores have four 

 flagella and a pulsating vacuole. Draw an empty cell. 



4. Sexual reproduction. Study a filament in which the cells have devel- 

 oped a large number (eight, sixteen, or thirty-two) small gametes of equal size 

 (planogametes). Draw part of the filament showing some cells empty and some 

 with gametes. The gametes have only two flagella. 



5. Observe the conjugation of the gametes to form zoozygospores. Draw 

 and describe. In order to bring out the flagella more clearly, stain with iodin 

 solution. If the gametes do not conjugate some may round themselves off and 

 become resting spores. This is a case of parthenogenesis. 



6. Note. When the zygospore germinates it does not develop a new fila- 

 mentous plant, but gives rise to number of cells which develop as non-sexual 

 zoospores, and these escape and produce the filamentous plant. Ulotrix, there- 

 fore, along with many other thallophytes, has what is known as an alternation of 

 generations. 



XXIII. FucHs evanescens Ag. Class, Phaiophycece. Order, Fucales. Family, 

 Fucaceae. 



This brown alga is common along the Atlantic coast. It may be obtained 

 from dealers in botanical supplies, and preserved in alcohol or other solutions. 

 Various species of Fucus may be found fresh at fish stores in large cities, these 

 plants often being used as packing. The thallus is a large, flat, dichotomously 

 branching frond of a dark brown color, attached to various objects by means of 

 a disc-like holdfast. 



