450 



Dansk Botanisk Arkiv, Bd. 3. Nr. 1. 



20. Acrochætium spec. 



Howe anf Hoyt^) in 1916 

 described an Acrochætium affine 

 which is closely related to Collins' 

 Acr. Hoytii, described in "Rho- 

 dora", 1908, p. 134 and to the 

 two species Acr. robustum and 

 unipes described by me. They 

 made a thorough comparison be- 

 tween their new species and Col- 

 lins' and my plants and arrived 

 at the conclusion that: "there 

 seems to be no compelling reason 

 for the association of our plant 

 with any one of the three names 

 mentioned rather than with any 

 other of the three." 



Growing rather abundantly 

 upon a Dictyota, which I have 

 determined to be Dictyota indica, 

 I have once more found an Acro- 

 chætium (Fig. 419) which is closely 

 related to the above-mentioned 

 species, but which, nevertheless, 

 when more carefully examined, 

 shows differences from all four 

 species. 



As is characteristic of these 

 species the germinating spore of 

 the plant now found produces a 

 more or less obtuse process pene- 

 trating into the peripheral layer of 

 the host, reaching a length of about 

 28// (Fig. 419 a, b); the spore itself 

 remains lying upon the wall of the 

 host; its diameter reaches a maxi- 

 mum of about 16 [1. 

 ^) Howe, M. A. and W. D. Hoyt, Notes on some marine Algæ from the 



vicinity of Beaufort, North Carolina (Memoirs of the New York Bot. 



Garden, 6, 1916). 



Fig. 419. Acrochætium spec. 

 a and h, basal parts of plants, 

 c, upper part of a filament, d, small 

 part of the same, more magnified, 

 (a, 6, d, about 200 :1 ; c, about 140:1). 



