250 Howe: Phvcological studies 



probably generically different. It does not form a solid, coherent 

 thallus and nothing is said of a calcareous coating. Hornet (/. c, y 

 p. clix) refers this Siphonocladus voluticola provisionally to the 

 genus Gomontia, but states that this reference is doubtful owing to 

 the imperfect condition of the specimen. 



Petrosiphon may, without serious doubt, be placed in the family 

 Valoniaceae as that family is defined by J. Agardh * and by Wille f 

 and perhaps also in the Valoniaceae as more recently limited by 

 Oltmanns, X even though the genus Siphonocladus, with which we 

 have compared Petrosiphon, is by Oltmanns excluded from the 

 Valoniaceae and made the type of a separate family, the Siphono- 

 cladiaceae. But it may fairly be questioned, we think, whether the 

 proposed separation of the Siphonocladiaceae and Valoniaceae as 

 distinct families is not rather difficult and unnatural. The main 

 point of distinction, as pointed out by Oltmanns, appears to be the 

 existence of a " Hauptstamm " in the Siphonocladiaceae, which is 

 lacking in the Valoniaceae. The historical type of the genus 

 Siphonocladus, as described and figured by Schmitz, does indeed 

 show a " Hauptstamm," but in most of the species which have 

 since been referred to the genus by Hariot, § Bornet, || Reinbold, ^[ 

 and Svedelius,** the " Hauptstamm " is not readily distinguishable 

 unless, perhaps, in the little-known early stages of growth. In 

 the species described above under the name Siphonocladus rigidus, 

 a main axis is soon lost when dichotomies occur as shown in figure 

 i, but is evident when the branching is as shown in figure 2 ; never- 

 theless, both these types of branching are sometimes found in a 

 single tuft and represent, we believe, the variations of a single 

 species. 



The specimens from which the above descriptions of new algae 

 have been drawn, including the actual materials which have served 

 as a basis for the published photographs and drawings, are 

 deposited in the herbarium and museum of the New York Botan- 



*Till Alg. Syst. 5 : n, go. 18S7. 



f Eng. & Prantl, Nat. I'fianzenfam. i 2 : 145. 1S91. 



+ Morph. unci Biol, der Algen, 1 : 255, 269. 1904. 



§Jour. cie Hot. 1: 56. 1887. 



|| Jour, de Bot. 1 : 56. 1887 ; De-Toni, Syll. Alg. 1 : 35S, 359. 1889. 



• Hedwigia 37 : (88) Beibl. 1898. 



* Svenska Exped. till Magellanslanderna 3 : 304. f. j and//. jS. 1900. 



