48 DEFINITION AND CLASSIFICATION OF FRUITS. 



expansion into a new generation. Fruits of this kind have sometimes a very 

 complicated structure. In them we are able to distinguish a complex outer 

 coat, and within, the embryo with its tightly adherent covering, the latter 

 portion of the fruit being that which has from ancient times borne the name 

 of seed. Fruits thus come before us as a series of forms, of which the members 

 at opposite extremities of the series differ greatly, but are linked together by a 

 large number of intermediate forms. At one end of the chain we have the 

 unicellular fruits of the microscopic Desmids, at the other the fruits of the Cocoa- 

 nut, which is differentiated into seeds on the one hand and several envelopes on the 

 other, and is as large as a man's head. 



As already stated, the spermatoplasm acquires the composition and form whereon 

 its fertilizing power depends within the confines of certain special cells. Extreme 

 variety is, however, found to prevail in this connection. In some plants, especially 

 those which conduct the process of fertilization under water, the spermatoplasm 

 takes the form of minute particles usually furnished with special motile cilia to 

 enable them to swim about. These have received the name of spermatozoids. They 

 escape from the cell-chambers in which they were formed into the water, rush about 

 for a short time or are carried by currents in the water, and finally reach the 

 ooplasm, whereupon they place themselves in contact with it, and enter into combi- 

 nation with it in a manner which may best be likened to the merging together of 

 two drops of oil floating upon the surface of water. In another category of plants 

 the spermatoplasm does not escape from the cell in which it has been developed, 

 but this cell itself enters into combination with the oogonium as a whole, and a 

 possibility is afforded in a variety of ways for the two kinds of protoplasm to 

 coalesce within a single enveloping cell-membrane. A third category of plants is 

 remarkable for the fact that the spermatoplasm does not coalesce as a whole with 

 the ooplasm, only a portion of it passing to the ooplasm. 



The above prefatory remarks give some idea of the extreme variety which exists 

 in the processes of fertilization, and it is no easy matter to give a short and concise, 

 and at the same time accurate, presentation of the facts involved, especially if one 

 tries not to use more than is absolutely necessary the innumerable technical terms 

 invented in recent times. Even taking into account only the most important of the 

 phenomena above referred to, we find twelve different processes or types of fertiliza- 

 tion and fruit-formation, and it will be the object of the next chapter to present 

 these in order, beginning with the simplest cases and concluding with the most 

 complicated. 



It will materially conduce to clearness of exposition if, in considering these 

 phenomena, we adhere to the old classification into Cryptogams and Phanerogams, 

 which was introduced by Linnaeus. According to the etymology of the words, 

 Cryptogams are plants which are fertilized secretly, whilst in Phanerogams the 

 process of fertilization is apparent. Since the microscope has been perfected and 

 brought into common use this distinction has no doubt lost its significance. If, 

 however, we adopt a somewhat different interpretation of these terms, we may 



