EUPHYCOPHYTA 



179 



20- 



15- 



10- 



5 



_fi^ult$ sterile 



whilst attempts to produce hybrids by artificial fertilization have so 

 far met with no success. Schreiber (1930) found that the ratio of 

 male to female gametophytes was always 1:1, and he subsequently 

 showed that of the thirty-two zoospores produced in each spor- 

 angium, sixteen gave male and the 

 other sixteen female gametophytes. 

 The male gametophyte of L, reli- 

 giosa is reported to bear unilocular 

 and plurilocular sporangia, but this 

 is so abnormal and has never been 

 confirmed or reported for any other 

 species, that it can hardly be 

 accepted without further evidence. 

 The ova of L. saccharina are re- 

 ported to be capable of producing 

 dwarf filamentous diploid plants 

 which reproduce by means of 

 unilocular sporangia. If this is 

 confirmed it may be that here we 

 have an example of a reversion to a 

 primitive filamentous diploid pro- 

 genitor, a feature which might help 

 considerably in indicating their Fig- 10° Laminaria A, L. digitata, 



'' ^ marked thallus before growth in 



ancestry. summer. Bj L. digitata, marked thal- 



The most important character- lus after growth in summer. C, effect 



. . 01 ^ i_ ^- of temperature on fruiting of game- 



istics of the gametophytic genera- tophytes in L. digitata. After 



tion are : Schreiber.) 



(i) The male gametophyte always has smaller cells. 



(2) The male gametophyte always consists of more than three 

 cells whereas the female may consist of only one cell, the 

 oogonium. Under good nutrient conditions both become 

 much branched. 



(3) The antheridia are unicellular and produce only one 

 antherozoid. 



(4) Any cell of the female gametophyte may function as an 

 oogonium. 



(5) The male gametophyte degenerates after the gametes are 

 shed whereas the female gametophyte persists. 



The young sporophyte first produces numerous rhizoids of 

 limited growth, but these are later covered by a disc-shaped ex- 



DEC. JAN 



FEB. 



