Vaucheriacese 243 



now packed with green aplanospores, cause the affected spots to appear 

 strikingly green on the withered leaf (Maire, '08). There are numerous 

 nuclei in the branches of the coenocyte and, except at the colourless tips of 

 the branches, large numbers of parietal disc-shaped chloroplasts without 

 pyrenoids. Both starch and oil occur as reserves. Motile cells are unknown, 

 reproduction occurring only by the formation of numerous aplanospores, 

 which are minute ovoid gonidia, set free from the ends of the branched tubes 

 by a rupture caused by the swelling of the inner layer of the wall. 



Phytophysa is a partial parasite in the cortical parenchyma of the stems 

 of Pilea, an Urticaceous plant of Java, causing the formation of gall-like 

 excrescences. The Alga consists of a vesicular coenocyte of a deep green 

 colour, furnished with a thick wall and attaining a diameter of 2'5 mm. 

 Each vesicle is provided with a neck which projects towards the exterior of 

 the pustule and through which the aplanospores ultimately escape. Oil 

 globules and cellulose grains (?) are the reserves. Only the peripheral part 

 of the large vesicular coenocyte forms aplanospores, the inner part forming 

 a mass of sterile cells between which and the outer wall the developing 

 aplanospores become squeezed. 



Ostreobium is another genus which consists of a richly branched system 

 of ccenocytic tubes within the substance of the shells of marine bivalves or 

 in the branches of corals. Numerous aplanospores are formed in club-shaped 

 aplanosporangia developed at the extremities of the branches. These 

 germinate directly to form new tubes. 



The genera are : Phyllosiphon Kiihn, 1878 ; Phytophysa Weber van Bosse, 1890 ; 

 Ostreobium Bornet & Flahault, 1889. 



Phyllosiphon Arisari is found in the leaves of Arisarum vulgare in Europe, and in the 

 leaves of various Aroids in N. America and Java ; also on Arisarum simorrhinum in 

 Algeria, and on Arum macidatum near Luneville in France. Lagerheim ('92) described 

 Ph. maximus, Ph. Philodendri and Ph. Alocasise, from S. America. Phytophysa Treubii 

 is known only from Java. 



Ostreobium is known in Europe, N. America, Samoa, and New Zealand. Nadson ('00) 

 has stated that Ostreobium Queketii Born. & Flah. when growing in deep water develops the 

 red pigment of the Rhodophycese, and in this state is identical with Conocelis rosea Batters. 



Family Vaucheriacese. 



In this family the thallus consists of a single and rather sparingly 

 branched coenocyte which often attains a length of 20 to 30 cms. As a 

 general rule many of these filamentous thalli live as an intricate tangled 

 mass, forming a dense mat of a very deep green colour. The filaments increase 

 in length by apical growth and are in most cases attached to a substratum 

 by means of 'hold-fasts' or rhizoid-like branches. In Dichotomosiphon 

 (fig. 161) the filaments are dichotomonsly branched, each branch being 

 constricted at the base and at various points along its length. 



162 



