380 Harper .—Sexual Reproduction in Pyronema 
by noting that it is only the division of the cell-body as 
a whole which leads to tissue-formation. Nuclear division 
may occur without cell-division and consequent tissue- 
formation, and in the case of sporangia, asci, &c., nuclear 
division may be followed by cell-division without tissue- 
formation. Nuclear division without cell-division gives 
opportunity for growth of the cell-body but is not tissue- 
formation. 
In reproduction the relations are perhaps not so clear, 
Multinucleated cells reproduce by much the same type of 
division in Cladophora as do uninucleated cells in the conidio- 
phores of Erysiphe. For sexual reproduction multinucleated 
cells may return to the uninucleated condition as is presumably 
the case in the motile gametes of Botrydium and Acetabularia. 
But that this return to the uninucleated condition is not 
necessary for sexual reproduction is shown by the case of 
Pyronema. 
In this connexion it is interesting to note that Stevens (33) 
has recently described the fertilization in Albugo [Cystopus) 
Bliti as consisting in the fusion of multinucleated sex-cells. 
His account is entirely opposed to the results obtained by 
Wager (39) and Berlese (3) on other species of the same or 
closely related genera. If it is true that we have multinuclear 
fusions in the sexual cells of one species, and fusion of a single 
pair of sexual nuclei in those of another, it is further evidence of 
the close similarity between uninucleated and multinucleated 
cells. Stevens seems to take the view that his oospheres and 
antheridia are the equivalents of tissues, since he designates 
them respectively as compound oospheres and compound 
antheridia as compared with uninucleated cells with the same 
function. He does not, however, discuss the question speci¬ 
fically, and his use of the term compound is not entirely clear 
in this connexion. For example, he does not call attention 
to the multinucleated conidia of the Albugo as compound 
conidia, though from analogy he might be expected to do so. 
In asexual reproduction by swarm-spores we have both 
types of cells ; for example, uninucleated swarm-spores in 
