and Laboratory Methods. 2619 



LXVII. Salvviia itatans (L.) Hoff. Salvinia. 



Class, Hydropterides. Order, Salviniales. Family, Salviniacea;. 



This floating water fern grows readily in aquaria in greenhouses. 



Sporophyte. 



1. Draw an entire plant as it floats on the surface of the water, showing the 

 horizontal stem, the leaves, and the peculiar root-like leaves hanging down 

 from the underside. 



2. Take out some of the plants and throw them into the water. Note how 

 they nearly always turn right side up. 



3. Place a leaf on the slide and examine without cover-glass under low 

 power. Draw a part of the surface showing the peculiar hairs. What is their 

 use ? 



4. Mount one of the dissected, root-like leaves and sketch under low power. 



5. Ecological note. — Describe the various ways in which the sporophyte of 

 Salvinia is adapted to its environment. 



LXVII I. Isoetes melanopoda J. Gay. Black-based Quill wort. 



Class and order, Isoetales. Family, Isoetaceae. 



This quillwort may be found in moist prairies and overflowed fields in the 

 central states of the Mississippi valley. Fresh or herbarium specimens may be 

 used, and stems preserved in 70 per cent, alcohol. 



Sporophyte. 



1. Sketch and describe the entire sporophyte, showing leaves, short stem, 

 and roots. 



2. Study prepared slides or cut cross sections of stems in alcohol and draw, 

 showing the following structures : the two vertical furrows and two large lateral 

 lobes, the outer cortex and extensive parenchymatous tissue in which the cells 

 are arranged in radial rows, on the inner limits of this layer a zone of meristem- 

 atic cells, inside of this a layer of clear cells (the phloem, " prismatic layer ") 

 and in the center a xylem-cylinder from which bundles pass outward to the 

 leaves. 



LXIX. Sigillaria Sp, 



Order, Lepidophytales. Family, Sigillariaceae. 



Fossil impressions of the trunks of large, arboreous Sigillarias are com- 

 mon in the formations of the carboniferous period and may be seen in most 

 museums. 



1. Sketch the surface of part of a trunk of Sigillaria, showing the leaf scars 

 and the longitudinal fluting. 



2. Note. — The heterosporous pteridophytes of the present time are the rem- 

 nants of a once great group of plants which formed a characteristic vege- 

 tation before and during the carboniferous period, which ended millions of 

 years ago. 



