GLOSSARY, 



399 



"the disease declares itself in a wet year in a 

 lucerne field, the crop may be regarded as 

 lost. Living in the interior of the leaf the 

 mycelium emits conidiophora which cover 

 these with a white or grey lilac flock surface ; 

 the leaves attacked are discoloured, wither 

 and fall. 



Peronospora vici^ (mildew of the pea 

 and the vetch). — This mildew, which attacks 

 different specit-s of peas and beans, is dis- 

 tinguished by a dense lilac flock surface 

 formed on the leaves. The organs of pro- 

 pagation and dissemination are the same as 

 those of PerfiHOspora . 



Peronospora viTrcoLA (mildew of the 

 vine). — -This fungus has great analogy with 

 the r/n/fiijihthiirii. It prefers to gi'ow on 

 the leaves of the vine, but it also invades 

 the young branches, the flowers, and the 

 grapes. (Brown rot, grey rot, juicy rot.) 

 The leaves begin to gi-ow yellow on the at- 

 tacked vines, then the spots are intensified 

 and the vines assume a reddish-brown colour. 

 This fungus lives between the cells and the 

 parenchyma and on the under surface of the 

 leaf emits conidiophora from which the 

 conidia or summer spores are detached. 

 These ripen in a night and germinate as soon 

 ;w they fall on a leaf rendered moist by the 

 dew or by the rain ; they produce mobile 

 zoospores. After a sojourn of half an hour in 

 a drop of water, they fix themselves, emit a 

 germinative tube which pierces tlie epidermis 

 and penetrates into the interior of the leaf. 

 Late in the season, winter spores are formed 

 iu the leaves which renxaiu active and live 

 in the withered leaves. In the spring the 

 .spores spread the disease. Mildew appears 

 early in May and June. The disease is often 

 arrested after the first spring invasion by 

 the dry heat of summer, but only by a 

 heat of 20° C. (68° F.). If the air be moist 

 the disease spreads more energetically and 

 makes rapM progress. I'l-mnii.ijuira does not 

 rest like the l'}u/tniil,fli,,,ii in rlic perennial 

 state in the plant during wintt-r ; it forms 

 in autumn oospores iu the attacked organs 

 which hatch iu the spring and agahi start 

 the disease. The organs of dissemination are 

 especially the sunmier spores or conidia which 

 are formed liy tliousands on the tufts of 

 conidiophora (m the lower surface of the 

 leaves and during the whole summer. These 

 conidia, fortunately, are not endowed with 

 the .same vitality as the oospores. Cold and 

 dryness destroy them easily. Moisture, on 

 the contrary, keeps them alive, but however 

 great it may be, this moisture does not 

 .suffice to make them germinate. It not 

 only requires the direct contact of water 

 with this spore to cause germination, but a 

 surrounding temperature between 17° and 

 30° (62-6°-86° F. ). About 17° C. the conidia 

 take about two daj-s to hatch, from 25° to 30° 

 half an hour suffices. The fine drops of dew 

 in warm weather are especially favourable to 

 the hatching of the disease. Looking to the 

 great number of conidia formed, it will be 

 understood why, when the conditions are 

 favom-able to their germination, the invasion 



is so sudden and so general and why in 

 summer in dry weathei mildew causes no 

 damages. 



Phai.enides or Geomktrides.— Butter- 

 flies with a rugose body and large wings, 

 generally nocturnal. The caterpillars are 

 called geometers or arpeiiteuses, owing to 

 their method of walking in the form of an 

 inverse U. 



Phoma tabifica (beet and mangel rot). — 

 The disease of the heart of the beet is in 

 certain cases the result of the invasion of a 

 fungus. It reaches its height in September. 

 In August leaves appear on the beet which 

 droop as if faded and finally wither more or 

 less completely. That is due to damage to 

 the petiole of the leaf, which shows over a 

 great part of its length a whitish withered 

 spot surrounded by a brown aureole. The 

 disorganization is propagated, following the 

 bundles, as far as the heart of the beet and 

 kills the whole of the young nascent leaves. 



Phylloxera of the Vine. Phylloxera 

 vastatrtc (aerial and subterranean). ^The 

 adult female lays a single egg on the wood 

 of the aerial part of the vine called a winter 

 Qgg. The young apterous phyllo.xera which 

 issues from it either immediately gains the 

 roots or the leaves of the vine, on which it 

 produces a characteristic gall doing little in- 

 jury to the plant. This aerial form or galli- 

 cole of the phylloxera is rarely found on 

 French vines, but it is very widely spread 

 on American vines, the roots of which are 

 not generally invaded by the insect. The 

 aerial form of the phylloxera does not belong 

 to the indispensable cycle of the very curious 

 evolution of this insect. The young phyl- 

 loxeras which descend to the roots prefer to 

 fix on the radicles to introduce their dart 

 there and to remain fixed at the same spot, 

 continually sucking the juice of the plant. 

 By this constant irritation, first the bark 

 sweUs, then hypertrophy of the cambium, 

 hence the formation of tumefactions. After 

 the death of the phylloxera these nodosities 

 rot and cause the decomposition of the root. 

 The large number of phylloxeras fixed on 

 all the roots rapidly cau.se atrophy of the 

 radicular system, and by that fact alone the 

 vine languishes even in the first year and 

 may die in the second. The phylloxeras 

 of the roots are always females or rather 

 partlienogenetic subjects which breeil with- 

 out sexual intercourse. Each individual 

 lays daily -30-40 eggs or geminations, the 

 eggs of which hatch in eight days. Twenty 

 days after their birth they are reproduced 

 in the .same way. With 6-8 parthenogenetic 

 generations yearly an individual may repro- 

 duce thirty million descendants. Among.st 

 the last gemmation of summer there are eggs 

 which give birth to a new winged form which 

 abandons the roots, ascends the plants, and 

 disperses itself in the vineyard. This form is 

 also parthenogenetic ; it lays on the aerial part 

 of the plant four eggs which hatch new sexual 

 forms, male ami female. These individuals 

 are deprived of digestive organs and do not 

 therefore take nourishment. Coupling oc- 



