NOTICES OF BOOKS. 503 
to the Physiologist, and we will allow the author to speak in his 
own words. He states (at p. 9 to 11.) :—‘ The spontaneous divi- 
sion of the frond is included by some writers amongst the modes 
of reproduction; but this is not strictly correct, for it is rather 
the manner in which the individual plant grows, since all the cells 
arrive at maturity nearly at the same period and terminate their 
existence about the same time. The Zesmidiez, are most probably 
reproduced only in two modes; one by the escape of the granu- 
lar contents of the mature frond, and the other by the formation 
of sporangia, the result of the coupling of the cells. When the 
cells approach maturity, molecular movements may be at times 
noticed in their contents, precisely similar to what has been de- 
scribed by Agardh and others, as occurring in the Conferve. This 
movement has been aptly termed a swarming. It has been seen 
by numerous observers,—in this country by Messrs. Dalrymple, 
Jenner, Thwaites, Sidebotham, Dr. Dickie and others. The cause 
of this sudden commotion cannot be ascertained ; but I have met 
with it more frequently in specimens that have been kept some 
days than in fresh gathered ones. When released by the opening 
of the suture, the granules will still move, but more rapidly and 
to a greater distance. With the subsequent history of these gra- 
nules I am altogether unacquainted, but I conclude that it is simi- 
lar to what has been traced in other Algæ. The second mode of 
reproduction is by coupling, and the formation of sporangia. A 
communication is established between two cells, and a seedlike 
mass is formed in the same manner as in the Conjugate. This is | 
green and granular at first, but soons becomes of a homogeneous 
appearance and of a brown, or even reddish colour. There are - 
however some variations in the process in the two families which 
require notice. In the Conjugate, the cells conjugate whilst still 
forming parts of a filament; but in the Desmidiee, the filamen- 
tous species almost invariably separate into single joints before 
their conjugation, and in most of the species the valves of the 
cells become detached after they are emptied of their contents. In 
many genera the sporangia remain smooth and unaltered; in 
others they become granulated, tuberculated, or spinous; the spines 
