EUPHYCOPHYTA l8l 



Stratum. Subsequent growth of the stipe takes place in the outer 

 layer of the medulla, and in the adult organ five regions can be re- 

 cognized : 



(i) Primary fixing organ. 



(2) The bulb. 



(3) A flattened twisted area said to provide additional rigidity. 



(4) A portion with flounced edges. 



(5) A flat straight portion that passes into the lamina. 



The existence of these structures is supposed to be correlated 

 with the large lamina which is cleft into many linear segments. 



If, as sometimes happens, the whole of the plant is torn away 

 with the exception of the bulb, this organ is still capable of repro- 

 duction and assimilation. The advanced external differentiation of 

 the stipe is not reflected in its histology where the diflerentiation is 

 poor because there is no secondary growing region, no mucilage 

 ducts, and trumpet hyphae are not conspicuous. 



The male gametophyte is filamentous whilst the female fre- 

 quently consists of only one cell which functions as the oogonium. 

 After fertiUzation has taken place the development of the sporo- 

 phyte to maturity in both species requires only one year so that the 

 plants are true annuals. Saccorhiza polyschides is found on the 

 Atlantic coasts of North and West Europe whereas the other 

 species, 5. dermatodeay is circumpolar and is possibly the parent 

 species from which the other developed, a speculation which is 

 further supported by the fact that 5. dermatodea is more primitive 

 because the stipe is not twisted nor are the edges so wavy. The 

 young sporophyte first develops a juvenile blade which does not 

 bear sporangia and then a new and thicker basal fertile blade is 

 intercalated, but it is only the juvenile blade that bears the crypto- 

 stomata. 



Laminariaceae: Thalassiophyllum (thalassto, sea; phyllum, leaf). 

 Fig. 102 

 The perennial sporophyte is apparently composed of a spirally 

 twisted, fan-shaped lamina unrolling from a one-sided scroll with- 

 out any mid-rib. A study of the embryonal stages, however, shows 

 that the young plant is flat and bilaterally symmetrical. The two 

 edges then curl up and the plant tears down the centre giving rise 

 to two lateral scrolls each unrolling from a thickened outer margin, 

 but as one of the scrolls soon ceases to develop the mature plant 



