AN ENCYCLOPEDIA OF HORTICULTURE. 



121 



Phytophthora continued. 



examination, the starch grains are found to be dissolved 

 and fissured. Where the tuber has not passed beyond 

 the first stage of disease, it shows little sign of injury 

 externally; and such tubers are often used for planting 

 for next year's crop, with the frequent result of diseased 

 plants growing from them. So far it may be said that 

 all mycologists are agreed in regard to the development 

 of this Fungus ; but what remains to be stated here is 

 still hotly discussed. Globular cells, three or four times 

 the diameter of the mycelium, possessing a thick, warty 

 outer coat, and a thin inner one, were observed in 

 diseased potatoes, even as early as 1845. Mr. W. 6. 

 Smith has found such bodies very abundantly in old 

 potatoes, and in diseased leaves kept in a vessel over 

 water (i.e., in moist air) ; and has observed, in regard 

 to them, a process of development like that in Peronospora 

 nivea, &c. ; and he asserts that these brown, globular 

 cells are the resting-spores of the Potato-disease Fungus. 

 This is denied by Prof. De Bary, of Strasbourg, and 

 by others. Mr. A. S. Wilson has brought forward a 

 theory, with reasons in support of it, connecting with 

 the Potato-disease Fungus numerous small, oval bodies 

 (that are white by reflected, and dark by transmitted, 

 light), which are very abundantly scattered through the 

 tissues of Potato-leaves, Ac. He and Mr. Smith believe 

 that they have traced these small bodies into actual 

 connection with the undoubted mycelium of P. infestans. 

 The bodies, on analysis, are found to consist largely of 

 particles of oxalate of lime, with a basis of protoplasm. 

 Mr. Wilson regards them as a resting condition, analogous 

 to the sclerotia of other Fungi, e.g., that of Peziza postvma, 

 in its uses to the Phytophthora. The true nature of the 

 bodies has been hotly discussed in the " Gardeners' 

 Chronicle " during the years 1883-85. Mr. Wilson regards 

 Potatoes as almost all infected throughout their tissues 

 by these resting masses of the Fungus, which, he con- 

 siders, emit mycelium, and give rise to disease, under 

 conditions favourable to the growth of the Fungus. 

 Much has been written on remedies for the Potato disease ; 

 yet it can hardly be said that any methods have 

 been discovered really efficient in securing the Potato 

 crop against this scourge. Beyond doubt, the unnatural 

 conditions induced by continuous cultivation and pro- 

 pagation from the tubers, have rendered the plants a 

 more easy prey to the Fungus, and more liable to suffer 

 severely from its attacks, than uncultivated plants would 

 be; and this is seen if the effects on the Potato are 

 contrasted with those on the Bitter-sweet, a plant also 

 occasionally attacked by the Fungus. Prevention is best 

 promoted by selecting, as seed tubers, varieties known 

 to resist disease, since some are much hardier than 

 others in this respect. The soil should be well drained, 

 and there should be free circulation of air around the 

 plants, to promote evaporation, since moisture, confined 

 air, and warmth, promote the rapid growth of the Fungus. 

 The seed tubers should be planted uncut, or the cut 

 surfaces should be allowed to heal, or may be seared 

 with a hot iron, or otherwise coated over, before being 

 put into the soil. All tubers that show traces of disease, 

 and all dead stalks, leaves, &c., should be burned, to 

 prevent the propagation of the disease through them. 

 Of recent years, Mr. Jensen, of Copenhagen, has strongly 

 advocated " protective moulding," and his views have been 

 stated and supported at some length by Mr. C. B. 

 Plowright, in the " Gardeners' Chronicle." The system 

 was also suggested by Dr. Lang, in 1858 ; but it has not 

 been generally adopted. Mr. Jensen's method may be 

 briefly summarised as follows: The ground should be 

 thoroughly worked and quite friable, and the potatoes 

 should be planted in rows about 30in. apart. The first 

 moulding should be about 4in. high, and flat on top. The 

 protective moulding should be done as soon as diseased 

 spots appear on the plants, and, in any case, should not 



VoL IIL 



Phytophthora continued. 



be deferred later than the time of Wheat-harvest : it is 

 effected, on a small scale, in gardens, by the use of a hoe ; 

 on a large scale, in fields, by a specially-formed plough. 

 The layer of earth should be, when it has settled down, 

 not less than 4in. thick along each side of the row, above 

 the tubers. At the same time, the tops should be 

 bent over to one side of the row, and allowed to wither; 

 and they may then be cut off and removed. The tubers 

 may be lifted in about a week after the removal of the 

 tops. This system proceeds on the belief that the tubers 

 are infected by conidia and zoospores washed by showers 

 from the leaves and through the soil on to the tubers, 

 and not by mycelium through the stalk. Mr. Jensen 

 also recommends disinfecting the seed tubers by storing 

 them for four or five hours in a dry-air chamber, at 

 a temperature of from lOOdeg. to lOodeg. Fahr. Of 

 course, other host-plants of the Fungus, whether wild or 

 cultivated, ought not to be grown in the neighbourhood 

 of Potatoes. Attempts have been made to substitute 

 some other species of tuber-forming Solanum for 8. tube- 

 rosum, but without great success. The most promising 

 seem to be S. Commersoni and 8. Maglia, the former of 

 which appears to be uninjured by P. infestans. 



PHTTOPTTTS. See Kites. 



PHTTOZZS (of Sprengel). A synonym of Sphacele 

 (which see). 



PT ATC.A M-j-nTTp (from piaros, fat, and anthos, a 

 flower ; alluding to the shape of the blossoms). ORD. 

 Asclepiadeae. A genus comprising, perhaps, half-a-dozen 

 species of greenhouse succulents, with low, deeply four- 

 jointed stems, natives of South Africa. Flowers mediocre, 

 often fasciculate; calyx small, five-parted; corolla cam- 

 pannlate, deeply five-cut, the lobes narrow, acuminate, 

 valvate ; corona lobes five, inflexed. The species have 

 the general habit of Stapelia (which see for culture). 

 P. pnllns (dark-flowered), /f. three or four together ; corolla dark 



purple, the segments lanceolate, silky above, replicate. August. 



Branches usually hexagonal, erect ; angles a little sinuated, 



having strong, spreading teeth, h. 6in. 1774. (B. M. 164d) 

 F. geminatus (twinX The correct name of plant described in 



this work a* Fixiunllif* nominal 'a. 



PICEA (from pix, pitch ; the trees produce abundance 

 of resin). Silver Fir. STN. Abies (of Don). Including 

 Veitchia. OBD. Coniferae. A genus comprising about a 

 dozen species of mostly hardy, evergreen trees, inhabit- 

 ing the extra-tropical regions of the Northern hemisphere. 

 Flowers monoecious. Leaves acicnlar, spirally scattered, 

 with the midrib prominently qnadrigonal or sub-terete, 

 contracted into a very short, articulated, persistent petiole. 

 Cones ovoid or oblong-cylindrical, erect or horizontally 

 spreading ; the bracts not falling away from the axis at 

 maturity, as in Abies. Owing to a succession of blunders 

 in works treating on Conifers, the generic names Abies 

 and Picea are generally transposed. For culture, see 

 Abies. 



P. ajaaensls (Ajona). shoots glabrous when young, yellowish- 

 brown, marked with oblong, smooth, prominent cushions. L, 

 those on the side shoots in many rows, but twisted at the base 

 so as to be all in the same horizontal plane; on the upper 

 surface of the branch appressed, parallel in direction to the 

 branch ; all flattish, linear-oblong, rather obtuse, not spine- 

 tipped ; upper surface three-ribbed; underneath, one-ribbed. 

 cones erect, lin. to 2in. long, fin. broad, oblong, tapering to 

 each end ; scales shining-brown, oblong-ovate, h. 70ft. toSMt 

 Japan, 1861. A beautiful Fir, resembling P. extelsa, but more 

 elegant. SYN. Abies AUoquiana, of gardens. (B. M. 6743 ; G. C. 

 n.77xviiL 185.) 



P. alba (whiteX* White Spruce, young shoots very glaucous. 

 1. less numerous, longer, and more pointed than in other species, 

 somewhat glaucous, scattered around the branches, erect, quad- 

 rangular, cones oblong-cylindrical, light brown, small when 

 ripe ; scales loose and thin, round or bluntly pointed, with en- 

 tire edges, h. 30ft to 40ft Canada. Ac., 1700. (F. d. S. 

 2251.) 



P. Alcoqnlana (Alcock's).* young shoots covered with long, weak 

 hairs. 7., those on the leader shoots appressed ; on the lateral, 

 given off on all sides ; all rigid, more or less curved, linear 



