Lecture XV. 119 



secondary protoplasmic connections among the cortical cells. 

 Once in the auxiliary cell the segment of the oosperm-nucleus 

 divides repeatedly and some of its segments move into buds 

 formed on the surface of that cell. These buds become the 

 origin of short filaments, the terminal cells of which enlarge, be- 

 come ovoid and are called carpospores. The mass of carpo- 

 spores so formed is enclosed in the receptacle formed by the 

 filaments enclosing the procarp. An opening is left into this 

 fructification or cystocarp, as it is called, at the pole towards 

 which the cortical filaments converge and through it the carpo- 

 spores are set free when they mature. 



Plants bearing tetrasporangia do not produce antheridia or 

 carpogonia. Neither do sexual plants produce tetrasporangia. 

 It is evidently of great interest to ascertain how the two forms of 

 Polysiphonia are related. Observation has brought to light the 

 surprising fact that a plant bearing tetrasporangia never gives rise 

 normally to one bearing tetrasporangia. Similarly a sexual plant 

 never produces from its carpospores a sexual plant. The adage 

 that " like begets like " is strikingly contradicted by the life-history 

 of Polysiphonia. 



The carpospores are set free usually in the late summer or 

 autumn. They germinate immediately and give rise to plants 

 which do not attain their full size before the winter. In the 

 following spring they continue their growth and begin the 

 formation of reproductive organs in May, and about June form 

 tetrasporangia. The tetraspores are set free in July and germinate 

 forthwith. The plants arising from them mature quickly, and in 

 August form antheridia and carpogonia. The carpospores arising 

 from these are set free from the cystocarps in August or September, 

 and so the cycle is completed. Inasmuch as the life-cycle is not 

 wholly controlled by seasonal changes, the life-histories of all 

 individuals in one locality do not synchronise with one another, 

 and one often finds tetrasporic plants and carposporic plants out 

 of season ; but the calendar given above is that which has been 

 noted in a series of carefully observed cultures. The want of 

 simultaneity, however, in no way interferes with the sequence of 

 the different stages and in no case has it been found that a car- 

 pospore gives rise to a carposporic plant. A regular alternation 

 is the rule. A carposporic plant bearing sexual organs, antheridia 

 and carpogonia and producing carpospores, is developed from a 

 tetraspore. While a plant producing tetrasporangia containing 

 tetraspores is the outcome of a carpospore. The line of descent 

 is thus a regular alternation of sexual plants and asexual plants. 



