Fig. 152 Phyllosiphon arisari. A, leaf of Arisarum vulgar e with 



whitened patches due to attack of alga. B, portion of thallus ( x 66). 



(A, after Fritsch; B, after Smith.) 



the Siphonales and assigned to the Heterosiphonales. Fur^ermore, 

 in the Siphonales it presented other anomalous features in its mode 

 of reproduction. The thallus is composed of richly branched 

 threads ramifying in the intercellular spaces of the host. As a result 

 of the presence of the endophyte the chloroplasts of the host cells 

 do not develop and yellow-green patches occur on the leaf, whilst 

 at the same time the adjacent cells may be stimulated to active 

 division resulting in gall formation, but later on the affected cells 

 die. Reproduction takes place by means of oval aplanospores, which 

 in the case of P. deformans arise after the previous differentiation 

 of cysts. 



Botrydiaceae: Botrydtum (a small cluster). Fig. 153 



This genus belongs to the Heterosiphonales and is analogous to a 

 form such as Protosiphon, the commonest species, Botrydtum granu- 

 latum^ being frequently confused with it, especially as these two 

 plants are often associated on areas of drying mud. B. granulatum 

 makes its appearance during the warmer part of the year when it is 

 seen that the green, pear-shaped vesicles are rooted by means of 

 colourless, dichotomously branched rhizoids. The membrane is 

 composed of cellulose and the Hning cytoplasm contains numerous 

 nuclei scattered throughout it, whilst the chloroplasts, containing 

 pyrenoid-like bodies, are confined to the aerial part. The shape of 



264 



