74 PLANT PHYSIOLOGY 



4. Are parasites and saprophytes ever beneficial to man? 



5. Trace the development of the gametophyte from the Thallophytes to 

 the Spermatophytes. 



6. What is the biogenetic law? Illustrate. 



7. Which is more important, structure or function? Why? 



8. Does the scion ever have any effect upon the stock or the stock upon 

 the scion in a graft? (See Chap. XXX and the article by Hofman.) 



REFERENCES 



Breazeale, J. F. — The absorption of carbon by the roots of plants. J. Ag. 



Res., 26:303, 1923. 

 Hofman, Fred W. — Reciprocal effects from grafting. J. Ag. Res., 34:673, 



1927. 

 Nuttall, G. — Symbiosis in plants and animals. Nature, 112:657, 1923. 

 Withycombe, C. — The function of the bladder in Utricularia vulgaris L. — 



Proc. Linn. Soc., 46:401, 1924. 

 Young, P. A. — Classification of plants on the basis of parasitism. Am. Jour. 



BoL, 14:481, 1927. 



