7° 



LECTURE V. 



organs (/) are exclusively formed on others — a division of labour which is 

 elsewhere met with only in highly organised plants. In the species of Fucus, on 



the other hand, there is generally 

 no segmentation into leaf and axisj 

 and the branched shoots are them- 

 selves flat, or even band-shaped, 

 like the cladodes of many Phane- 

 rogams. In many other genera 

 of Algse are found richly branched 

 shoots without any flat tissue- 

 plates whatever ; the assimilating 

 chlorophyll lies beneath the sur- 

 face of the cylindrical body of tis- 

 sue (Fig. 68), the physiological 

 behaviour of which may very well 

 be compared with the shoot sys- 

 tem of Spartium junceum or of 

 Psilotum. Again, in other cases 

 the whole shoot consists of a short 

 rooted basal portion, on which are 

 situated leaf-like, thin plates of 

 tissue (Fig. 69), from the margin 

 of which similar organs often 

 grow forth, like the segments 

 of an Opuniia. I must unfor- 

 tunately deny myself in this su- 

 perficial survey, from going more 

 deeply into the variety of forms 

 prevailing here ; since just those 

 organographical relations which 

 are most important for us could 

 only be rendered clear by means 

 of numerous drawings and de- 

 tailed descriptions. On account 

 of their importance, however, 

 mention must finally be made of 

 those Algae the growth of which 

 is not accompanied by cell-divi- 

 sion, and which thus, as one is 

 accustomed to say, only consist 

 of one cell : this, however, does 

 not prevent these plants occa- 

 sionally attaining considerable 

 magnitude, and, in addition to the formation of roots, the most varied segmentation 

 of their shoots also. In this sense the genera Caulerpa, Boirydium, Vaucheria, and 

 others (cp. p. 4) have already been referred to. 



Fig, 66, — Lantinaria Clattstoni. 



