144 
to distinguish the Peronosporinse from other parasites. Pollen tubes 
inside of tissues are the only bodies likely to be confounded with them, 
and this only in case of species with much reduced haustoria. 
The haustoria have the same structure as the mycelium and their 
shape and varying size always furnish excellent data for distinction 
of species. They are sometimes so minute as to have thus far escaped 
the attention of botanists, e. g ., Phytophthora infestans , described 
in all the books as destitute of haustoria, possesses numerous ones 
which are extremely minute and filiform. Haustoria are simple or 
branched: (a) Simple and oval or spherical ( Cystopus candidus , Plas- 
mopara viticola. PI. epilobii, Pcronospora leptosperma , etc.); (b) Clav- 
iform and simple ( Premia lactucw ); (c) filiform and simple (P. myoso- 
tidis , P. 8'chleideni, P. affinis , P. clilorce , Phytophora infestans ); (d) 
ramified and claviform (P. parasitica ); (e) ramified and filiform (P. 
arborescens, P. calotheca , etc.). Ordinarily the haustoria have a double 
envelope and between these two envelopes irregular and voluminous 
masses of callose often occur and sometimes rupture the exterior mem¬ 
brane ( Cystopus candidus , P. myosotidis , etc.). At other times the exte¬ 
rior membrane shows only cellulose and incloses little callose. It then 
forms a complete sheath around the haustorium which can be removed 
in connection with the mycelium by a slight traction (P. JSchlcidcni). 
Sometimes the masses of callose formed by the haustoria are so abun¬ 
dant that they fill the entire cavity of the cell, the protoplasm being 
crowded against the wall. 
Masses of callose in a state of purity are also found in the cavity of 
the conidiophores. They take the form of rings or irregular plugs, 
of most variable location. In any case these plugs can not be likened 
to the septa which form at the base of the sporangium of the Mucorinse, 
as has been done. The only part of the conidiophores where the pres¬ 
ence of callose is constant is the base of the conidia where this substance 
plays an important role in the dissemination of the spores. 
To sum up, the constant presence of callose in the mycelium of the 
Peronosporinse enables us to recognize with great clearness the least 
traces of these parasites in the host plants and to show clearly the rela¬ 
tions which exist between the latter and the parasite. 
(4) This paper is really a continuation of the last one. Observations 
on the formation and the separation of the conidia in Cystopus candidus 
led M. Mangin to the following conclusions: The septum first appears 
as a delicate ring of callose on the thin inner wall of the basidium. 
This ring gradually enlarges until only a small central opening remains. 
The septum then appears as a funnel minus its tube, the convexity of 
which projects toward the base of.the basidium. The open central por¬ 
tion of the septum finally closes. About this time or a little sooner the 
thin cellulose wall of the basidium disappears at the level of the callose 
(is absorbed) and a constriction rapidly takes place, the base of the 
new conidium and the summit of the basidium rounding off by the 
