24 OUR NATIVE FERNS AND THEIR ALLIES. 



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

 Anthcridium in Ferns. In Torrey Bulletin, xm, 49-52, with 

 Plate LIV. (Apr. 1886.) 



The Development of the Ostrich fern. /;/ Memoirs 



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

 vn. (Apr. 1887.) 



On the Prothallium and Embryo of Osmunda Clay- 

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

 49-94, pi. lll-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 m:-isses 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. 



