HOW TO KNOW THE SEAWEEDS 



23a Gonimoblast placenta of relatively large, vacuolate cells and with 



nutritive filaments extending into the pericarp. Fig. 38 



GracilaTia verrucosa 



Figure 38 



Fig. 38. Gracilaria sp. 



A vertical section through a cystocarp showing the large-celled 

 central gonimoblast placenta from which nutritive filaments extend 

 out into the wall of the cystocarp (pericarp). The opening at the top 

 of the cystocarp is the ostiole. Carpospores are seen being produced 

 from the outer cells of the gonimoblast. Most of the species of Graci- 

 laria are more or less flattened (See Fig. 233) but one common cylindrical 

 one is G. verrucosa (Greville) Papenfuss which may be found both along 

 the Atlantic and Pacific coasts. It has been exploited commercially 

 as a source of agar although the product obtained is of a lower 

 quality than that obtained from species of Gelidium. 



42 



