Sunlight upon Aquatic Plants. 381 
of zygospores (West, 1. c., p. 36 ), it does so probably 
because it is acting injuriously upon the vegetative filaments, 
for conjugation appears to be induced in Conjugatae, when 
the external or internal conditions are becoming unfavourable 
in some way or other. That conjugation might exercise 
an after stimulating effect upon neighbouring non-conjugating 
cells, arousing them to increased vegetative activity, is not 
impossible, provided that plasmatic connexions existed, or 
that a plasmatic transference were proved to take place 
through the partition-walls of neighbouring cells of the same 
filament. This has not yet, however, been demonstrated in 
these plants, and the occurrence of lateral conjugation by 
special conjugating tubes connecting neighbouring cells of 
the same filaments renders the existence of any such inter- 
protoplasmic communication extremely improbable. Physio- 
logically, each adult cell of a Spirogyra - filament appears 
to be a distinct individual. The fact that when conjugation 
takes place, the activity of the neighbouring cells appears 
also to be increased, may simply indicate that the same 
causes which are inducing conjugation in certain cells are 
stimulating others to an increased vital activity manifested 
in other ways. Recent research has shown that injuries and 
injurious agencies generally, if not too severe, may cause 
an increased respiration, an increased production of heat, 
a commencement or increase in the rapidity of rotation, and 
generally may cause a more marked and active conversion 
of potential energy into kinetic, while upon the primary 
processes of constructive metabolism, at any rate as regards 
C0 2 -assimilation, the reverse effect is produced 1 . In many 
cases the energy liberated is partially expressed in the form 
of an increased growth activity, precise determinations of 
which have been given by Townsend and the writer in certain 
special cases 2 . An increased katabolism, however, involves 
1 Richards, Ann. of Bot,, Vol. x, 1896, p. 531, Vol. xi, March, 1897, p. 29 ; 
Ewart, Ann. of Bot., Vol. xi, Sept., 1897, p. 447, &c. 
2 Townsend, Ann. of Bot., 1897, p. 509; Ewart, Ann. du Jard. bot. de Buiten- 
zorg, 1898, Vol. xv, p. 198, &c. 
