188 PHYLUM IV. SIPHONOPHYCEAE 
‘ branching tubes, whose cavities are continuous through- 
out. They usually grow between the cells of their hosts, 
and draw nourishment from them by means of little 
branches (haustoria), which thrust them- 
- selves through the walls. 
277. The asexual spores (conidia) are 
produced upon branches (conidiophores) 
which protude through the epidermis of 
Fig. 78.—Plasmopara the host. In the Downy Mildews (Per- 
bits er onospora, Phytophthora, Plasmopara, 
etc. )these branches find their way through the breath- 
ing-pores and bear their spores singly upon lateral branch- 
lets; in the White Rusts (Albugo) the conidia-bearing 
branches collect under the epidermis and rup- 
ture it. Here the conidia are borne in chains ff 
ess 
or bead-like rows. PA ff 
278. In some genera the relationship to the ¢ 
Water Molds is shown by the fact that these 
conidia upon falling into water become true fy. 79, 
sporangia, within which few to many zoospores “2¥s® 
are produced. These after a free-swimming period be- 
come motionless and germinate by means of a tube which 
bores its way into the host. In two genera, however 
(Bremia and Peronospora), the conidia themselves germ- 
inate directly by a tube. 
279. The sexual reproduction takes place in the inter- 
cellular spaces of the host. Lateral branches of two kinds 
appear upon the hyphae; those of one kind (the young 
oogones) become greatly thickened and finally assume a 
globular shape; the other branches (the young antherids) 
become elongated and club-shaped, both becoming sepa- 
rated from the main filament by cross partitions. ‘The 
antherid comes in contact with the oogone which it 
penetrates by a tube, through which fertilization occurs, 
