MALE FERN. YOUNG SPOROPHORE. 211 



Having thus gained a knowledge of the position of the several 

 parts relatively to one another, and to the prothallus, in the case 

 of a young Fern plant of considerable size, younger plants may 

 successively be taken, and by a comparison of these the mode of 

 development of the young embryo, or Fern plant, may be 

 traced. In order to make preparations so as to show the several 

 parts of the embryo, sections should be made either from fresh 

 material, or better from material prepared with picric acid, and 

 hardened in alcohol, as above directed for the prothalli. The 

 direction of section should be parallel to the organic axis of the 

 prothallus, and perpendicular to the flattened surfaces : in such 

 sections, including embryos of suitable age, the stem, cotyledon, 

 root, and foot may all be observed ; further, the origin of these 

 several parts from definite segments of the fertilised oosphere 

 may be traced. For details as to the sequence of cell-divisions in 

 the first stages of development of the embryo reference should be 

 made to Text-books. 



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