Valonieae 253 



which are arranged with great regularity, form haptera which fasten the 

 neighbouring segments together. Dictyosphteria is therefore not really a 

 branched thallus, but rather a dense aggregate 

 or colony of similar ccenocytes held together 

 in a compact manner by haptera (called by 

 Murray & Boodle 'tenacula'). The interior 

 of this colony becomes hollow with its in- 

 creasing growth, and eventually the colony 

 bursts, forming an irregularly lobed thallus 

 which may reach 12 cms. across. In this genus 

 there are curious internal spines projecting 

 from the walls of the coenocytes into their 

 central cavities. Fig. 163. A young plant of Dictyo- 



The chloroplasts are rounded- polygonal and 

 contain from 1 to 3 pyrenoids (Murray, '93 ; 

 Kuckuck, '07 ; Borgesen, 13). In the protoplasmic layer there are starch- 

 grains and amylum bodies. The walls of the co3nocytes are tough and 

 elastic, and often striated on their outer -surfaces. 



The zoogonidia of Valonia are furnished with two ( V. utricularis) or four 

 (V. macrophysa) cilia and a red pigment-spot. They escape through 

 numerous perforations in the wall of the coenocyte, and germinate almost at 

 once. Arnoldi ('13) has observed pyriform zoogonidia about 8 10 p in 

 length in Dictyosphteria favulosa. Borgesen ('13) did not find any zoospore- 

 formation in large numbers of the W. Indian plants he examined, and he 

 suggests that in some cases the young plants arise from aplanospores. He 

 considers that most of the young plants arise from small lentiform cells 

 which are loosened and set free from the thallus of other individuals. 



The genera are : Valonia Ginnani, 1757, and Dictyosphseria Decaisne, 1842. Both are 

 widely distributed in tropical and subtropical seas, and are especially abundant in the 

 West Indies. They occur attached to rocks and stones, and also as epiphytes on other 

 Algse. They are almost equally abundant in shallow and in deep water, extending to a 

 depth of from 30 to 40 metres. Dictyosphezria favulosa occurs frequently in shallow 

 water on coral-reefs where it is constantly under the influence of the waves. In these 

 situations it remains more or less globular and attains a diameter of about 5 cms. ; on the 

 other hand, in deep water (40 metres), where it is also often abundant, it becomes a flat 

 expansion up to 12 cms. in diameter. 



The swollen coenocyte of Valonia ventricosa attains the size of a pigeon's egg or even 

 of a small hen's egg. After death the plants become detached from the substratum, the 

 green colour disappears, and they float away as translucent bladders. In this state they 

 are often drifted ashore in the Bermudas and have received the name of ' sea-bottles ' 

 (Murray, '95). 



NOTE : The genus Blastophysa Reinke ['88 ; '89 (inclus. Phteophila 

 Hansgirg, 1890)], which is an epiphyte on the thallus of various larger marine 



