92 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



they are produced on other joints, as well as on those which 

 give rise to the spores. It is curious, in two such closely 

 allied Algte as Vaucheria sessilis and V. clavata, to find 

 the fruit so very different. The spore of the former is per- 

 fectly inactive, while that of the latter revolves by means 

 of delicate cilia covering its whole surface. It is clear, then, 

 that we must not, in these lower Cryptogams, attach too much 

 importance to motion. Neither in these cases, nor in similar 

 organisms in the animal world, is there the slightest reason to 

 believe that this motion is effected by any system of muscles. 

 Its real cause is, at present, beyond our powers of discovery. 



70. Dr. Itzigsohn has figured in Hedwigia, 1852, p. 7, the 

 spermatozoa of Spirogyra arcta as produced within little cells, 

 after the fashion of those in mosses, and forming a little spiral, 

 with a thickened extremity. Whether there is any mistake 

 in this or not must be left to future observations ; the structure 

 in other cases, which he mentions as probable, viz., Vaucheria, 

 CEdogoniwm, Bulbochcete, and Cladophora, is, where it has 

 been ascertained, certainly very different, and resembles, more 

 or less, that in the higher Algfe, or the bodies are not sperma- 

 tozoids at all, but zoospores. 



71. It is to be mentioned, moreover, in connexion with the 

 sul)ject, that different Algae in different stages of growth wear 

 so different an appearance as to seem to indicate totally diffe- 

 rent affinities. Lenfianea torulosa, for instance, for a long time 

 has all the appearance of a Conferva,* in which condition its 

 nearest affinities could not so much as be suspected; the earliest 

 stages of Porphyra resemble a Bangia, and so of other cases. 

 This alone may lead to perplexity in such determinations, but 

 much more the fact that it is very doubtful how far many of 

 the supjjosed Alga, such as Glwodapsa, are autonomous species. 

 Where a plant bears fruit, and is reproduced by that fruit, as for 

 instance, Protococcus pluvialis (Fig. 8, 9), there can be little 

 doubt that a species is true ; but where all the propagation 

 is a simple repetition of the division of the endochrome, as in 

 Glceocapsa, there is some room for doubt. Mr. Thwaites, in the 



* Linn. Tr., vol. xx. p. 399. 



