MARINE BIOLOGICAL STATION AT PORT ERIN. 41 



two clearly differentiated forms of reproductive cells, viz. : 

 (a) motile gonidia (asexual), and (b) motile gametes (sexual). 

 Observations on Pylaiella during the spring and summer months 

 have revealed a periodicity or rhythmic alternation of these 

 reproductive cells, comparable with that found by Professor 

 Lloyd Williams in Dictyota dichotoma. 



" There is also a very definite cycle of development of 

 Pylaiella plants on the three ' hosts.' At the time when the 

 first gametangial stage has been reached by the Pylaiella growing 

 on Ascophyllum, nodosum, the young plants are just making 

 their first appearance on the now rapidly-growing plants of 

 Fucus vesiculosus. At a later period one can detect the embryo 

 plants of Pylaiella on Fucus serratus. The cycle is then 

 completed by the development of young plants on the new 

 shoots of Ascophyllum, whose maturer parts bear the now 

 battered and decrepit older generation of Pylaiella. 



"It is proposed to continue the research along these 

 lines : — 



(a) Systematic observation of the behaviour of Pylaiella 



during the winter. 



(b) Investigation of the cytological changes underlying 



the alternation of sexual and asexual reproductive 

 cells. 



(c) The relation of the epiphyte to the ' host ' plant." 



Plankton Investigation. 



In the course of the plankton work, which is carried out 

 continuously at Port Erin, there has been this year one special 

 investigation which may be briefly described. It has been 

 much discussed in the past whether the plankton is so regularly 

 distributed that two hauls of the same net, taken at the same 

 place and, as nearly as possible, simultaneously, will give 



