ECTOCARPALES 



139 



haploid sporangia and are most abundant in spring and early 

 summer. Fig. 92 is a schema taken from Knight (1923) to illustrate 

 the life cycle as found in English plants during the course of one 

 year. 



EcTOCARPACEAE : Phaeostromu {phaeo, brown; stroma, mattress). 



Fig. 93- 

 This is cited as an example of a much reduced ectocarpoid form 

 which occurs as an epiphyte or partial parasite upon marine grasses, 

 such as Zostera, or else upon other brown algae. 



Fig. 93. Phaeostroma Bertholdi. Thallus ramifying in Scytosiphon showing 

 sporangia {s) and a hair {h). (After Oltmanns.) 



Mesogloiaceae : Mesogloia {meso, middle; gloia, shme). Fig. 94. 



In this and related genera {Castagnea, Eudesme, Chordaria and 

 Acrothrix) the construction is of the "cable" or consolidated type 

 described by Church (1920) in which there are one or more erect 

 parallel strands enclosed in a mucous matrix, the whole being 

 interwoven with lateral branches. There are three principal zones 

 that can be recognized in the plant thallus : 



(a) a medulla composed either of one long thread accompanied 

 by offshoots of the first order or else of a group of long threads ; 



{h) a cortex of peripheral assimilatory filaments and colourless 

 hairs ; 



{c) a subcortex composed of offshoots from the medulla. 



