HORSETAILS. 139 



sure to have a well-formed and uninjured specimen. 

 Observe the peculiar structure of the cells that compose 

 the sporangium wall. Ascertain, if you can, how the 

 sporangium opens.^ Draw carefully a few of the cells, 

 using the high power. 



IV. Examine the spores under the high power of the 

 compound microscope, mounting some of them in water 

 and others dry. How do the dry ones differ from those in 

 water? Breathe gently on them, and see if any changes 

 take place. Draw one or more of the spores with their 

 slender, hygroscopic appendages, slaters. 



V. Sow some of the spores in water and others on moist 

 soil, and at intervals examine with the microscope. Germi- 

 nation of the spores and the early stages of development 

 of the prothallium are easily observed, and should be figured 

 and described. 



Sterile Frond. 



I. Examine specimens of the sterile frond throughout, 

 comparing them in detail with the fertile ones. How do 

 they differ from the latter in size, color, texture, formation 

 of branches, and structure on transverse section? Is 

 there a " division of labor " ? If so, point out what you 

 conceive to be the most important function of the fertile 

 frond; of the sterile frond. 



II. Study the fibro-vascular bundles, and compare with 

 those of the fertile frond. Verify the details of structure 

 as given by Goebel, Outlines of Classification and Special 

 Morphology, pp. 270-272. 



'Cf. Newcombe, Spore-dissemination of Equisetum, Bot. Gaz., Vol. 

 Xm (1888), p. 173. 



