INTRODUCTION. 



THE vegetable kingdom may be divided into five groups more or less closely 

 related to one another : Thallophytes, Muscineae (Bryophytes), Vascular Cryptogams 

 (Pteridophytes), Gymnosperms, and Angiosperms. The examination of these groups 

 in the following pages will show that the names here given to them by no means 

 happily express their characteristic and distinctive features. This is especially true 

 of the Thallophytes and Vascular Cryptogams; the vegetative body in the Thallo- 

 phytes is not always a thallus, and true vessels are found, so far as we know at 

 present, only in two forms among the Vascular Cryptogams. These five subdivisions 

 have been grouped together to form higher divisions in different ways at different 

 times. They have been distributed for instance into Thallophytes, that is, plants 

 whose vegetative body is described as a thallus, because it commonly shows no differ- 

 entiation into stem, leaf and root, such as we observe in the higher plants, and into 

 Cormophytes, or plants with stems and lateral members ; but this division rests on 

 purely external and by no means constant marks, and is therefore of no systematic 

 value. The division again into Cryptogams including Thallophytes, Muscineae and 

 Vascular Cryptogams, and Phanerogams comprising Gymnosperms and Angiosperms, 

 is out of date now that we know the relations of the Gymnosperms and Angiosperms 

 to the Vascular Cryptogams. Nevertheless the Gymnosperms and Angiosperms will 

 be considered in the present work as forming one division under the name of seed- 

 plants (Spermaphytes) whose characteristic mark is that they form seeds. It would 

 perhaps be more in accordance with modem views to class the Gymnosperms with 

 the Vascular Cryptogams, for these two groups agree in all essential characters 

 except in the forming of seeds and in the mode of fertilisation, which is by pollen- 

 tubes in the Gymnosperms, by spermatozoids in the Vascular Cryptogams; the 

 method of sexual reproduction especially is the same in both. But it will be 

 found to conduce to clearness and simplicity of statement if we consider Gymno- 

 sperms in connection with Angiosperms. The mode of formation of the female 

 sexual organs is the same in the Muscineae, the Vascular Cryptogams and the 

 Gymnosperms ; these organs are here termed archegonia, and accordingly these 

 three divisions will be included under the term Archegoniatae. It would be thoroughly 

 in accordance with our present knowledge to divide the forms of the Vegetable King- 

 dom into Thallophytes, Archegoniatae and Angiosperms. The mutual connection 

 however of the several divisions must be discussed later when we are considering 

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