INTRODUCTION. 3 



(Fungi) ; and Algals (Confervse, Seaweeds, etc.) ; so 

 that Sea-weeds are nearly, not quite, the lowest forms 

 of vegetable organization. Numerous freshwater Algae 

 and the large families of Diatomacem and Desmidiacem 

 are lower still, and for the present at least must be con- 

 sidered to be at the base of the scale. 



Having thus traced the humble relationship of Sea- 

 weeds to their kindred plants, I proceed to describe the 

 peculiarities on which that relationship is based. In 

 doing so I shall draw largely on Dr. Harvey's admirable 

 introduction to his ' Nereis Boreali- Americana,' and I 

 take this opportunity to record my deep sense of grati- 

 tude for the information that I have derived from that 

 valuable Essay on this interesting but difficult subject. 



All plants are composed of cells variously developed, 

 according to the functions they have to perform in the 

 formation of roots, wood, bark, stems, leaves, or flowers. 



In Plowering-plants and Ferns, vascular plants as 

 they are called in consequence of the presence of vas- 

 cular tissue in their structure, the cells assume many 

 varieties of form and substance ; but in cellular plants. 

 Mosses, Lichens, Fungi, and Algae, they are more uni- 

 form and simple, and in Algae, including of course Sea- 

 weeds, they are all of the same nature as those found in 

 the soft parts, the leaves for instance of plants of the 

 higher orders. 



In the Vegetable Kingdom there are however no hard 

 lines of demarcation-; the descent from the highest to the 

 lowest form is gradual, and the arrangement of the cells 

 in the more perfect Sea-weeds, though different from, is 

 still analogous with that observed in vascular plants. 

 Organs similar to roots, stems, and leaves are still pre- 

 sent, and are furnished with different series of cells, 



b2 



