SEA WEEDS 357 



firmly held ; but some of the smaller species grow attached to 

 larger weeds, into the substance of which they frequently penetrate ; 

 and it is possible that these derive some amount of nourishment 

 from the sap of their supporters. Some are of a recumbent nature, 

 being attached to the rock throughout their whole length, while 

 others are so incrusted with carbonate of lime which has been 

 extracted from the water that they resemble corals rather than 

 forms of vegetable life. Nearly all of them contain a bright-red 

 colouring matter in addition to the chlorophyll by which they are 

 enabled to feed on carbonic acid gas. 



None of the rhodosperms are of really microscopic dimensions, 

 and they all grow by the repeated division of the cells of the apex, 

 while the branches are derived by the similar division of new cells 

 at the sides. 



All plants are particularly interesting during the period of 

 fruiting, and this is remarkably the case with many of our red- 

 spored sea weeds, which are brighter and prettier while laden with 

 their spore-producing cells ; and the collector of marine algee should 

 always endeavour to obtain as many species as possible in fruit, not 

 only on account of the brighter appearance that may characterise 

 them at this time, but mainly because the opportunity of studying 

 the mode of reproduction should not be missed. 



In the rhodosperms the reproduction may be either asexual or 

 sexual. In the former case fertile spores are produced without the 

 necessity for any outside fertilising element, and four are usually 

 produced in each one of the sporangia, hence they are generally 

 known as tetraspores. Where the reproduction is of the sexual 

 type, the male cells are produced singly in the terminal cells of the 

 fronds, and since they are usually crowded together in consider- 

 able numbers, and contain none of the red colouring matter that 

 exists in the other parts of the plant, their presence is easily 

 observed. 



The female cells (carpogonia) are also produced on the tips of 

 the branches, and when the male elements escape from their cells, 

 they are conveyed passively by the movements of the water, for they 

 have no vibratile cilia by which they are propelled, and on coming 

 into contact with the female cell they adhere closely. An opening 

 is then formed in the latter, and the male element enters the 

 carpogonium, which germinates, deriving its nourishment from 

 the parent plant, and the spores are thus formed. Lastly, it is 

 interesting to note that the asexual spores, the male cells, and 



