BOTANY 



of these spores after escaping from the sporangium gives rise to a mycelium, which 

 penetrates the tissues of a leaf. The sporangium may also germinate directly 

 without undergoing division and form ing swarm -spores. A similar transformation 

 of sporangia into conidia is also found in other Peronosporcae as a result of their 

 transition from an aquatic to a terrestrial mode of life. 



rifii-ii/ii. an extremely destructive parasite, also produces copiously 

 branched sporangiophores and occa- 

 sions the "False Mildew" of the 

 leaves and fruit of the Grape-vine. 

 A Ibugo Candida ( = Cystojnis candidus), 

 another very common species, occurs 

 on ( 'rncil'erae. in particular on fiijixi-lfn 

 blttrmpcutoris, causing wliite swellings 

 on the stems. In tliis species the 

 sporangia are formed in long chains 

 on the branches of the mycelium 

 under the epidermis of the host plant. 

 and produce numerous .swarm-spores. 

 The sexual organs of the Perono- 

 sporeae resemble those of the genus 

 raucheriu. (Fig. 292). They arise 

 within the host plant the oogonia as 

 spherical swellings of the ends of 

 certain hyph.v, the antheridia as 

 tube-like outgrowths arising as a 

 rule just below the oogonia. Both 

 are cut off by transverse walls and 

 are multinucleate (Fig. 321). The 

 several species exhibit interesting 

 differences as regards the nuclear 

 changes. In Ptfonospora /i>/i-n.<///<-n, 

 Albuyu Candida, and A. Lcpigom, l'[i- 

 t/iiniii. rinfitiii/tni'ti. ami Sdtrospora, 

 a single large central egg-cell or 

 oosphere becomes differentiated in 

 the protoplasm of the oogoninm ; this 

 contains a single nucleus in a central 

 position, while the remaining nuclei 

 p ass j nto t l, e peripheral layer of pro- 

 t lasm (perf.^,,,). Theantheridium 



of a 



Ki<;. 3-JO.-.I. Surface vi.'u ,,f th- epi 



Mntu 1,-i.f. with ipc^opfaorai of fhntorhtho,-,' 



in/Man* projecting t'rnni the atomata ( x (HI); ;;. 



, ,i,,- iponngfam; C, anotl.-r in proceM of now sends a process into the oogonmm, 



division ; /), a swnnn-srxMH. (;,-/> x 540.) which at its apex opens into the 



oosphere and allows a single male 



nucleus to pass into the latter (Fig. 321, 2). The oosphere then becomes surrounded 

 with a cell wall (Fig. 321, 3), and nuclear fusion takes place, while the periplasni 

 is utilised in forming the outer membrane of the spore (episporium). In Perono- 

 sj>orn fiu ?< i sit! i-i< the ripe oospore has a single nucleus, in Albuyo it becomes 

 multinucleate as a result of nuclear division. In J/6 <// I'liti and A. pvrtulacac 

 there is also a central oosphere surrounded by periplasm, but the oosphere contains 

 numerous nuclei, which fuse in pairs with a number of male nuclei entering from 

 the anthoridium. A multinucleate oosporo thus arises from the compound egg-cell. 



