30 



MANUAL OF BOTANY 



the separating walls are present, so that the filament is divided 

 into a number of chambers, which are not cells but coenocytes. 



This coenocytic structure may extend into some of the mor- 

 phologically most highly complex bodies. Thus the Alga 

 Caulerpa, which attains considerable size and whose body shows 

 rounded stems and much-divided leaves, is composed of only a 

 single coenocj'te, whose cavity extends through all the ramifica- 

 tions of the plant. The Fungus Mucor muceclo shows a similar 

 structure {fig. 780). 



In cases where the Thallophyte is composed of masses of 



Fig. 780. 



Fi'j. 78U. Cueuocyte of Mucor miicedo. 



cells there may be considerable histological differentiation, or 

 there may be but little. In some of the brown seaweeds we find 

 a limiting layer, enclosing a very different internal tissue. 

 In some this is composed of elongated loosely arranged cells 

 with mucilaginous cell walls ; in others it shows differentiation 

 into more complex structures. Tlius in Macrocystis we find 

 under the epidermal layer a layer of thin-walled parenchyma 

 covering a layer of somewhat prosenchymatous cells with 

 thickened walls, sometimes with pits upon them. The inner 

 portion of this contains the well-marked sieve tubes already 

 referred to. Some of the large Algae of the same group as 



