324 



FUNGI 



of life on the host is extensive destruction of the tissues, usually ending 

 in death. Hypertrophy is produced in other cases, especially at the 

 time of the formation of oosperms, leading to swellings and distortions 

 of the parts affected. 



Of the species of Pythium (Pringsh.) transferred to this order by 

 de Bary (Bot. Zeit., 1881) from the Saprolegnieae, some are saprophytes 

 inhabiting the dead bodies of both plants and animals, while others 

 are both parasites and saprophytes. 



The oogones are globular cells with either a smooth or a granulated 

 wall of some thickness, situated, as a rule, terminally, or more rarely 

 interstitially. Soon after separation by a transverse wall from the hypha 

 which bears it, the protoplasm of the oogone, which is rich in drops 



Fig. 286. — Fertilisation of Peronosporeae. /. — VI., PytJiiu7!i gj'acile Schtvk. Successive stages accord- 

 ing to numbers (x about 800). VII .,Peronosp07-a arborebcetis de By. Oosphere is invested with a ; 

 thick membrane, outside of which is the periplasm contracting to form outer coat of oosperm ( x 600). 

 (After de Bary.) 



of fatty matter, begins to collect into a central mass containing the 

 drops and bounded by a hyaline layer. Outside this central body 

 {oosphere) there is left over a clear mass of protoplasm {periplasvi)^ which 

 fills up the space between it and the wall. AVhile the oogone is thus 

 developing, the antherid arises, either from the pedicel-cell of the oogone 

 itself, or as the terminal cell of a neighbouring branch. It has commonly 

 the form of an irregularly bent tube with an unthickened cell-wall, and 

 at first ordinarily granular protoplasm. It applies itself closely to the 

 wall of the oogone, and sends through it a delicate straight impregnating 

 tube, which penetrates to the surface of the oosphere. The protoplasm 

 of the antherid also undergoes about this period a differentiation into 

 two masses ; one, threadlike but irregular, and occupying the middle. 



