6 GEIfEEAL HISTORY OF THE INFTJSOEIA. 



Desmidieae are known to move through considerable spaces. They travel 

 towards the light ; appear on the side of the vessel on which the Hght falls, 

 or rise to the surface and form a peUicle upon it. These, and the analogous 

 fact of their penetrating to the surface of mud in which they have been 

 imbedded, when exposed to light, are phenomena common to the Desmidiea? 

 with other Algae. ''Another proof (writes Mr. Ealfs) of their power of 

 locomotion is afforded by their retiring in some instances beneath the siui'ace 

 when the pools diy up," a phenomenon witnessed also in the case of other 

 plants. Braun {R. S. p. 203) casually refers to this kind of motion, dependent 

 on the resumption of vital action. The Penium curtum {Cosmarium curtum, 

 Ralfs), which grows '' in rain-pools which are altemately quickly filled and 

 dried up in the changes of the weather, ascends from the muddy bottom, 

 when the pools fill, in the form of beautiful bright green clouds, produced 

 by the social growth and the very fluid, widely- extended gelatinous invest- 

 ment of the cells." The movement of this plant, it is added, is more active 

 and more regular than that of other Desmidieae, and "it is a remarkable 

 sight to behold all the individuals in a dish of water in a short time turn 

 their long axes towards the hght, and thus arrange themselves in beautiful 

 streaks in the gelatinous mass. Observation likewise shows that it is the 

 younger haK of the cell, distinguishable as such for a long time after division, 

 which here turns towards the hght." 



Contents of Feonds. — The contents of the fronds or frustules of Desmidieae 

 are designated generally by the name of Endochrome. This endochrome, we 

 have already remarked, is of a grass-green colour, and contained in a proper 

 sac hning the denser lorica. It is not homogeneous, but presents nmnerous 

 globules, small vesicles, and many refracting coipuscles ; it is commonly 

 not unifonnly diffused, but collected in a definite manner, and it either com- 

 pletely fills its sac or leaves it unoccupied at parts, which not seldom are 

 constant in position and aspect. The appearance of the endochrome is 

 modified by age, by external physical circumstances, and by the process of 

 development. Nageh and Braun describe it as constituting two layers 

 within the primordial utricle, viz. an outer and an inner mucilaginous layer, 

 the latter the thicker of the two. 



Ehrenberg, influenced by his behef of the animal natiu^e of the Desmidiaceae, 

 and by his pecuhar h}^3othesis of their polygastric organization, represented 

 the larger vesicles or globules to be digestive sacs or stomachs, and the 

 smaller green corpuscles, ova. He even exerted his imagination still fiu-ther, 

 by announcing that in Micrasterias, Arthrodes^nns, and one or two other 

 genera, male reproductive stmctiu^es are visible. These suppositions it is 

 not necessary to disciiss, seeing that they are unsupported by any facts in 

 the stnictiu'e and oeconomy of this family. 



The globules and corpuscles of the endochrome of Desmidieae seem to 

 differ in no respect from those in other Algae, consisting of chlorophyll, 

 starch, and of oily materials floating in a wateiy medium. In most species 

 of Closterium and of Tetmemorns, some large diaphanous vesicles are con- 

 spicuous, either disposed irregularly, or more frequently in a single longi- 

 tudinal series (II. 1, 12, 13). These have the appearance of being distinct 

 cells ; and Mrs. Thomas has indeed described two such, of large size, in 

 Cosmarium margaritiferum, as '' vesicles filled with mo\dng granules." No 

 doubt many of the apparent vesicles are nothing more than vacuoles which, 

 as in other protoplasmic substances, tend to arise in the ceU-contents, and 

 may assume a fixity in size and in position. 



The several species of Closterium and of Docidium, and some of Penium^ 

 present also, at each extremity of the endochrome (II. 2, 9, 14), '' a large 



