THE GREEN ALG^E 639 



pseudocilia consist of protoplasmic processes, and one is of 

 course tempted to look upon them as remnants of cilia, which 

 have become useless for their ordinary function — a view which 

 has fallen into disrepute of late years, chiefly because the 

 pseudocilia are not used for purposes of locomotion. There 

 would, however, seem to be some ground for regarding them 

 as derived from cilia, and this for the following reasons. In 

 Chlamydomonas Kleinii (Schmidle 59) we have a good example 

 of undoubted cilia persisting within the mucilage of a Palmella- 

 stage. In some of the Chlamydomonadineae (e.g. Hcematococcus, 

 Polytoma, and Chlamydoblepharis) the cilia of the mother-cell 

 persist up to the time of the liberation of the daughter-cells. 

 In a Tetraspora or Apiocystis this persistence of the cilia would 

 obtain throughout the whole colony derived from the germina- 

 tion of a motile zoospore, and the cilia would only be dis- 

 carded when a new motile element was to be formed. In the 

 division of a Tetraspora or Apiocystis cell within the mucilage 

 each daughter-cell is stated to receive one of the two pseudocilia 

 and forms the other de novo.' Keeping these facts in mind, it 

 seems not unlikely that in the pseudocilia of the Tetrasporaceae 

 we have the remains of actual cilia, which have become modified, 

 perhaps to serve some other function (respiration ?). This 

 view also receives some support from a study of the genus 

 Physocytium, which was discovered as an epiphyte on fresh- 

 water Algae by Borzi (10) but has not since been observed. 

 The organism (fig. 2, f) consists of globular colonies, which are 

 attached to the substratum by two delicate threads and contain 

 a few irregularly arranged cells. These ultimately acquire two 

 short cilia and become liberated as zoospores. After swarming 

 about for some time the latter become attached by the apices 

 of their cilia, a membrane appears around them, and they 

 subdivide to form a new colony. Here, therefore, the cilia 

 appear to serve directly as organs of attachment at the 

 termination of the motile phase — a function which they perform 

 in many other cases, although Physocytium is peculiar in their 

 subsequent persistence. 



Many authorities (Wille 68, Blackman and Tansley 6) include 

 a number of filamentous forms, generally more or less enveloped 

 by mucilage, among the Tetrasporaceae, and have suggested 

 that these forms indicate the direction of evolution of the higher 

 filamentous Algae. This is, however, to say the least, doubtful. 



