140 Bibliographical Notices. 



chacun des points de rupture. II y a dans ce cas, comme je 1'ai dit 

 ailleurs, de duplication simple. Dans les Desmidiees, il y a deduplica- 

 tion et re" duplication* 



" It is with unfeigned diffidence that I venture to dissent from the 

 opinion of one possessing so profound a knowledge of these tribes, 

 and I do so only from conviction, the result of close and repeated 

 investigations. 



" I have stated my belief that the same changes occur in both the 

 Desmidiece and the Nostochinece. A cell in Micrasterias has two he- 

 mispheres, just as a joint in Anabaina has ; in both these separate, 

 and in both each hemisphere becomes again a perfect sphere ; and if 

 in Micrasterias the two hemispheres were united by their whole 

 bases, there would not remain even an apparent difference between 

 them. 



" The form of the cylindrical cells no longer helps us in tracing 

 the method of division. In Penium as in the Conjugate, they seem 

 merely to elongate and then divide. As I formerly suggested, in a 

 paper read before the Botanical Society of Edinburgh, I consider it 

 extremely probable that in all the simple Algae the cell or joint con- 

 sists of two valves, and that additions occur at their junction, the 

 original parts remaining unaffected : but this it may never be pos- 

 sible to demonstrate satisfactorily, unless a species of Conferva with 

 a coloured integument should be detected, or some means can be 

 devised for permanently colouring the filaments without impairing 

 their growth. Then indeed the question might be determined ; at 

 present I can merely show the probability that the cell in cylindrical 

 species of Desmidiea agrees with the joint in a Zygnema or Tynda- 

 ridea ; since whenever the covering is colourless and free from mark- 

 ings not the slightest difference can be perceived. This is the case 

 in a few species of Penium ; and hence Penium Brebissonii is by some 

 authors placed in the Palmelleae. In Penium margaritaceum and Pe- 

 nium Cylindrus the integument is coloured, and we are enabled, by 

 means of the paler appearance of the newly- formed portions, to sa- 

 tisfy ourselves that in these also each half of the original cell is ac- 

 quiring during the division a new partner. In Didymoprium the 

 same fact is rendered apparent, because the suture passes between 

 minute teeth ; these teeth recede from each other, and the new teeth 

 which appear between them show the place where the separation of 

 the joint has occurred." 



To these interesting observations it may be added that the order 

 of development in Diatomacece, where the frustules adhere long 

 enough together to show their progress, is precisely the same. In 

 Isthmia, for instance, if the several segments of the thread be indi- 

 cated by symbols expressing the order of their development, the 

 same symbols would equally express the same phenomena in a 

 thread of Spheerozosma. 



Many other matters of interest are discussed in the Introduction, 

 such as the claims of these bodies to be ranked amongst vegetables, 

 the nature of the active molecules at the apex of the frustules of Clo- 

 sterium, the swarming of the articulations of Scenedesmus, the mode 



