242 



Siphonales 



('utricles') which form the cortical layer are contiguous but not adherent; whereas in 

 Pseudocodium the medullary filaments are longitudinally arranged and the branches of the 

 cortical layer are coherent, so that in a superficial view the cortex is hexagonally areolate. 

 Codium occurs in both the Eastern and Western hemispheres, but Pseudocodium is known 

 only in the temperate regions of the Eastern hemisphere. The plants are perennial, and 

 in Western Europe reproduction takes place freely in the winter. 



Family Phyllosiphonacese. 



This family includes some interesting endophytic or endozootic Alga? 

 which in most cases are partial parasites. 



The thallus of Phyllosiphon consists of a richly branched coenocyte 

 (fig. 156 B), the rather irregular tube-like ramifications of which traverse in 



Fig. 156. Phyllosiphon Arisari Kiihn. A, leaf of Arisarnm vulgare showing the diseased areas 

 caused by the Phyllosiphon ; B, branches of the Alga in the leaf-stalk, x 68 ; C, portion of 

 algal thallus with aplanospores, x 340 ; D, aplanospores, x 400. (From Wille, after Just.) 



every direction the intercellular spaces of the leaves and leaf-stalks of 

 various members of the Aracea?. Owing to this intrusion and the destructive 

 action of the invader, the leaves of the host soon display diseased areas 

 from 0'5 1 cm. in diameter, which often coalesce at their margins to 

 form larger patches (fig. 156 A). These patches are at first yellow owing 

 to the secretion of orange-yellow oleaginous droplets in the cells of the 

 host due to the stimulation of the parasite. When the leaf wilts the 

 oleaginous droplets disappear and the filaments of Phyllosiphon, which are 



