80 PRACTICAL BOTANY. 



This method of demonstration of the nuclei has the advantage 

 of simplicity, but the results are not permanent ; if it be desired 

 to obtain specimens for keeping, they should be stained, as above 

 directed, with methyl-green and 1 per cent, acetic acid ; or better 

 with hsematoxylin. 



Treat a zoogonidium, which has come to rest, with 

 a plasmolysing agent such as 2 per cent, solution of 

 common salt, watching it meanwhile under a high 

 power : the protoplasm will contract, and a fine cell- 

 wall will be seen. This result may also be obtained 

 by pressure on the cover-slip. 



Mount and examine zoogonidia which have already 

 come to rest, and by a comparison of them the process 

 of germination of the zoogonidia, and the development 

 of new plants from them may be deduced. 



For comparison with Vaucheria another member of the Siphoneae 

 may be examined, viz. Codium tomentosum, which is to be found 

 growing near low- water mark on rocky shores, and is an Alga of 

 very wide distribution, though not of very general occurrence on 

 the British coasts. 



Observe externally the cylindrical, green, spongy thallus, which 

 branches dichotomously, and is attached to the rocky substratum 

 by an extended disk. 



Transverse sections should be cut : if fresh material be used, 

 they may be mounted in sea- water ; if alcohol material, in weak 

 glycerine. Note, under a low power, the central felt of inter- 

 woven tubes, which are relatively narrow, and occasionally 

 septate : the peripheral part of the section is occupied by a band 

 of larger elongated sacs, arranged in a radiating manner. 



Tease out a small piece of the thallus gently with needles : it 

 will then be seen that the thallus consists of a system of branched 

 tubular sacs, similar to those of Vaucheria, but aggregated 

 together to form a spurious tissue, similar to that of the larger 

 Fungi 



