24 OUR NATIVE FERNS AND THEIR ALLIES. 



CAMPBELL (Douglas H.). On the Development of the 

 Antheridium in Ferns. In Torrey Bulletin, ..xill, 49-52, with 

 Plate LIV. (Apr. 1886.) 



: The Development of the Ostrich fern. In Memoirs 

 Boston Society of Natural History, iv, 17-52, with Plates IV- 

 vii. (Apr. 1887.) 



On the Prothallium and Embryo of Osmunda Clay- 



toniana L. and O. cinnamomea L. In Annals of Botany, vi, 

 49-94, pi. m-vi (1892). 



CHAPTER V. 

 FERN STRUCTURE. 



Be it ours to meditate, 



And to the beautiful order of thy works 

 Learn to conform the order of our lives. 



BRYANT. 



69. Tissues. The life-history of every plant commences 

 in a single cell, and all the complications of vegetable growth 

 depend on two simple processes, viz., the enlargement of indi- 

 vidual cells to their full size, and their multiplication by divi- 

 sion. The lowest forms of vegetable life consist of a single 

 cell, either globular or elongate. Those of a somewhat higher 

 grade consist of a single row of cells, or at most a single layer; 

 while still higher forms of growth consist of masses of cells 

 variously grouped together and specialized by differentiation 

 from the typical form and character. 



70. Cells become specialized or set apart to fulfil a certain 

 function in the economy of plant growth in many ways. Some 

 are lengthened for giving strength to stems or leaves; some 

 have their walls thickened to give rigidity or hardness where 

 protection is needed from injury to more delicate structures 

 within ; and some are variously adapted for containing and dis- 

 tributing the secretions or other fluids connected with the cir- 

 culatory system of plant life. Seven distinct varieties of tissues 

 are recognized by structural botanists, yet some of these are 

 connected with each other by various gradations, 



