

Fig. 135 Harvey ella and Holmsella. A-E, stages in development of 

 gonimoblasts after fertilization in Harveyella mirahilis. a = auxiliary 

 cell, s = sterile filaments. F, filaments of parasite, Holmsella pachy- 

 dermay in host. G, antheridia of Harveyella mirabilis. H, tetraspores 

 in Holmsella pachyderma. e= tracks left after tetraspores have 

 escaped, s = sterile cells, t — tetraspores in various stages, te = 

 escaping tetraspores. (After Sturch.) 



are said to pass through the full floridean life cycle twice every year. 

 It is clear that their much reduced morphological features are to be 

 associated with the parasitic habit, and have arisen as a result of the 

 adoption of parasitism. The position of the genus has been the 

 subject of controversy. In the past it has been placed in the Gigar- 

 tinales, but is now more generally placed in the Cryptonemiales. 



GiGARTINALES 



Thallus construction in this order can be either of the central 

 filament or fountain type, but it is often so modified in the adult 

 plant that it is difficult to interpret. The support cell or an ordinary 

 intercalary cell is set aside before fertilization to act as the auxihary 

 cell. 



GiGARTiNACEAE : Gtgarttna (Gtgarton, grape stone). Fig. 136 



This is a widespread genus, the species of which are often diffi- 

 cult to determine taxonomically. The plants, several of which arise 

 from a prostrate disc, vary greatly in habit from large, fiat, little- 

 branched, foliose expansions (G. atropurpurea) to terete fronds that 

 are irregularly pinnate or dichotomously branched. The female 



242 



