122 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



especially by Kiitzing (1843, 1849), to receive various genera belonging to the 

 siphonous complex, among which are the Sphaeropleaceae, Cladophoraceae, Va- 

 loniaceae, Caulerpaceae, and Dasycladaceae (a group comprised of calcified 

 plants that for a long time were thought to be corals). Stizenberger (1860) ar- 

 ranged the algae belonging to this complex in his order Siphophyceae (except 

 for the Sphaeropleaceae and Cladophoraceae, which he placed in the Conferva- 

 ceae of his order Nematophyceae). This order was comprised of the families 

 Valoniaceae (in which he included Caulerpa), Vaucheriaceae (now placed in 

 the Xanthophyceae of the Chrysophycophyta), Codiaceae, and Dasycladaceae. 



Schmitz (1879a) created the group Siphonocladaceae to receive his new genus 

 Siphonocladus and a number of other multinucleate septate or saccate genera 

 (e.g., Valojiia, Microdictyon, CludopJiora, and Botrydium, which genus is now 

 known to belong to the Xanthophyceae). 



Starting with Bohlin's paper of 1901, the complex of siphonous algae has 

 been segregated into six orders. Bohlin erected the order Vaucheriales and re- 

 moved it to the class Heterokontae. Blackman and Tansley (1902) substituted 

 the ordinal name Siphonales for the designation Siphophyceae or Siphoneae and 

 divided the order into the two suborders Siphoneae (which received nonseptate 

 genera) and the Siphonocladeae (which received septate forms such as Siphono- 

 cladus, CladopJwra, Yalonia, SpJiaeroplea, and many other genera). Oltmanns 

 (1904) elevated the suborder Siphonocladeae to the rank of order (Siphonocla- 

 dales) and placed in it the five families Siphonocladaceae, Cladophoraceae, 

 Sphaeropleaceae, Valoniaceae, and Dasycladaceae. 



West (1904) removed the Cladophoraceae and Sphaeropleaceae to an autono- 

 mous order Cladophorales. As characterized by him this order conformed closely 

 to Oltmanns' Siphonocladales and in 1916 West merged the Cladophorales in 

 the Siphonocladales. Heering (1921) and Oltmanns (1922a) not only followed 

 West but in conformity with Oltmanns' classification of 1904 extended the con- 

 cept of the Siphonocladales to include even the nonseptate Dasycladaceae. In 

 the intervening period, however, B0rgesen (1905, 1913) had discovered in Si- 

 phonocladus and related genera the peculiar method of cell division termed 

 segregative division by him. Despite the distinctiveness of this character dis- 

 agreement has persisted with respect to the autonomy of one or the other of 

 these two orders. Some authors (e.g., Fritsch, 1935, 1947) have accepted the 

 Cladophorales but place the genera comprising the Siphonocladales in the Si- 

 phonales, whereas others (e.g., Feldmann, 1938) have recognized the Siphonocla- 

 dales as a distinct order but have included in it the genera constituting the 

 Cladophorales. Egerod (1952) has given a careful analysis of this confusing 

 state of affairs and has detailed the evidence favoring recognition of all three 

 orders. 



As has been pointed out by Fritsch (1944) and Egerod (1952) the Anadyo- 

 menaceae (at least as far as Anadyomene and Microdictyon are concerned) de- 

 part from other Siphonocladales in not exhibiting segregative division. Both 

 these authors have also brought attention to the correspondence between this 

 family and the Cladophoraceae. The Anadyomenaceae are here transferred from 

 the Siphonocladales to the Cladophorales. 



In 1931 Pascher removed the Dasycladaceae from the Siphonocladaceae and 

 erected for them the order Dasycladales, a group distinguished by the formation 



