CHAPTER V 

 BLASTOCLADIALES 



This small order consists of the single family Blastocladiaceae 

 embracing about a dozen species in three genera. The forms 

 included agree in the possession of non-cellulose walls and 

 uniciliate swarmspores. The group is apparently most closely 

 related to the Monoblepharidales. It has been given ordinal 

 rank previously by Petersen (1910: 494) and von Minden (1916: 

 189). Other authors have incorporated its genera in the Sap- 

 rolegniales. The recent monograph of Kanouse (1927: 295) is 

 the best general treatment of the group. The members of the 

 order are typically aquatic. They occur as saprophytes on 

 submerged plant and animal substrata. In recent years a few 

 species have been isolated from the soil (Coker and Braxton, 

 1926: 146; Harvey, 1925: 162; 1928: 560). Of the three genera 

 included, Blastocladia and Alloniyces are clearly very closely 

 related. The third, Gonapodya, is somewhat less certainly a 

 member of the group. 



In Blastocladia and Alloniyces the thallus is differentiated 

 into a main thickened axis or trunk and slender branches, and 

 is attached to the substratum by branching rhizoids. In these 

 respects, relationship is indicated to both the Monoblepharidales 

 and the Leptomitaceae of the Saprolegniales. The similarity 

 to genera such as Araiospora and Rhipidium of the latter group 

 is pronounced. In Gonapodya there is no differentiation of the 

 thallus into a central thickened portion and slender branches, 

 and rhizoids are lacking. The thallus is composed of cylindrical 

 hyphae which are definitely and often frequently constricted as 

 in the Leptomitaceae, and cellulin plugs lie in the constrictions. 



Asexual reproduction takes place by means of swarmspores 

 borne in thin-walled sporangia or in peculiar thick-walled resting 

 sporangia. The thin-walled sporangium varies in shape from 

 ovoid to linear, and at maturity is provided with a single apical 

 exit papilla or with several scattered over its surface. The 

 sporangium is developed terminally, but further growth of the 



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