156 A TEXTBOOK OF THEORETICAL BOTANY 



which run at right angles to the surface of the whole disc. Growth is 

 effected by the formation of fresh rows of cells at the margin. 



The cells of the attaching disc, though containing chromoplasts, and 

 therefore capable of assimilation, are primarily storage organs and are packed 

 with flattened, discoid starch grains. These grains give a brown rather than 

 a blue colour with iodine, showing that the chemical constitution of the 

 starch is different from that in higher plants. It is known as floridean starch. 

 This starch is also found abundantly in the collecting and conducting 

 filaments of the stem. 



Sexual Reproduction 



Chondrus shows a clear alternation of generations between sexual and 

 asexual generations, though the plants are morphologically alike. The male 

 and female reproductive organs are borne on separate fronds. It is apparently 

 uncertain whether both types may arise from the same basal attachment, 

 though it is unlikelv. The tetrasporic plants occur chiefly in the winter. 



The sex organs consist of antheridia and carpogonia. The antheridia 

 are borne on small, slightly flattened segments in which the chromoplasts 

 are poorly developed so that the segments appear almost white. The female 

 organs are located in the central part of the upper ends of the vegetative 

 fronds, forming raised oval areas i to 2 mm. in length. The asexual repro- 

 ductive organs occur near the apices of the young fronds. They appear as 

 elongated, dark spots, accompanied by slight bulging of the assimilatory 

 layer. Such protruberances of the thallus, in which reproductive organs occur, 

 are termed nemathecia. 



The Antheridium 



The specialized segments of the thallus on which antheridia occur are 

 almost colourless, but their structure differs little from that of the vegetative 

 thallus. It is only the peripheral cells of the assimilatory filaments which 

 are modified. The last two or three cells of each filament are colourless 

 owing to the great reduction in the size of the chromoplasts. These two 

 or three cells constitute the male organ and each cell may be regarded as an 

 antheridium, for it gives rise to a single male gamete or spermatium (Fig, 

 144). This escapes as a colourless round mass of protoplasm devoid of any 

 cell wall or flagella. A fragment of the plastid is present but is not sufficient 

 to colour the gamete. The spermatia are shed from October to December. 



The Carpogonium 



The development of the female organ in Chondrus has not been fully 

 investigated, but so far as is known the process occurs as follows. Certain 

 segments of the upright fronds take on the function of forming the female 

 organs. In the early stage the central conducting tissue consists of slightly 



