Octoker 24, 1872. ] 



JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 



325 



enabled to move rapidly about. These bodies germinate 

 exactly in the same way as the ordinary spores, by discharging 

 their contents through the ruptured outer coat (l) , and must 

 play a very important part in the economy of the plant ; for it 

 is manifest that although they cannot move unless immersed 

 in fluid, yet it can easily be imagined that during rainy 

 weather, or after heavy dews, and when the leaves of Potato 

 plants are all wet and blown against each other by the wind, 

 a few zoospores, originating from two or three infected plants, 

 would speedily contaminate a large field of Potatoes : then, 

 when we remember the hundreds of thousands of ripe ordinary 

 spores blown about everywhere by the wind, their rapid germi- 

 nation, and immediate reproduction of other ripe spores and 

 new zoospores, the rapid and fatal spread of the murrain 

 remains no longer a mystery. 



Tig. 4. — Peronospora infestans, spore germinating, enlarged four hundred 

 diameters. 



Fi<j. 4 shows a section through the stalk of a Potato plant, 

 with a single mature spore germinating upon the surface, its 

 mycelium penetrating the epidermis (ir) and cortical layer (nn). 



Now, not only is Peronospora infestans able to reproduce 

 itself from its spores and zoospores, but amongst the mycelium 

 in the intercellular passages of spent Potatoes are found other 

 bodies which there grow and fructify. These bodies, dis- 

 covered by Dr. Pay en, though referred to the Sepedoniei by 

 Montagne (the order next in succession to Mucedines, to 

 which latter order the genus Peronospora belongs) , are con- 

 sidered by Berkeley and others to be probably a secondary 

 form of fruit (oospores) of the Potato fungus itself. These 

 bodies, named by Montague Artotrogus hydnosporus, are 



Kg. 5.— Artotrogus hydnosporus, enlarged four hundred diameters. 



shown in fig. 5 magnified four hundred diameters ; the young 

 Artotrogus being shown at o in its mother cell (with threads), 

 and at p free. 



These bodies make the study of the Potato disease more 

 complicated, and its ultimate eradication far more difficult ; 

 for they do not germinate at once (as do the spores and zoo- 

 spores), or perish, but remain quiescent for a whole season, 

 till certain favourable external conditions cause them to burst 

 from their sleep and reproduce the parent. Resting spores 

 and dormant sclerotioid tuberiform bodies are very common 

 amongst fungi, a very remarkable instance being found 

 amongst the Agaracini. In Agaricus tuberosus we have an 

 Agaric springing from a tuberiform base, which is invariably 

 found growing from the dead remains of the previous year's 

 fungi, generally the Russulas ; but we have found the sclerotia 

 at the bottom of the tubes of some of the Polyporei, the per- 

 fect Agarics emerging through the tubes. 



Closely allied to the Potato fungus is another species found 

 infecting Chickweed (Stellaria media), and named by Casparry 

 Peronospora alsinearum. In this species, and some others of 



the genus, male organs, or antheridia, have been detected, as 

 shown at q, fig. 6, where the mycelial filaments are shown 



Fig. 6. — Peronospora alsinearum, enlarged four hundred diameters. 



bearing the oogone, with which the mature antheridium is 

 shown in contact : the contents of these cells are interchanged, 

 and thus an oospore or resting spore is produced. At k is 

 shown a section with the inflated summit of the fecundating 

 tube of the antheridium (x) touching the gonosphere : this 

 latter has a neat outline, produced by the membrane of cellu- 

 lose which has just been secreted. 



At fig. 7 (s) is shown a ripe oospore, furnished with its 

 thick reticulated epispore, the surrounding protoplasm having 

 almost disappeared ; and at T a ripe oospore, whose epispore 

 has been detached by maceration in water ; a thick, colourless 

 endospore remaining, composed of two thick layers containing 

 protoplasm, with two unequal vacuities. The fecundating 

 tube may be seen still fixed in the endospore at u. These 

 oospores, or resting spores, of the Chickweed parasite, like 

 those of the Potato, possess the singular property of remaining 

 dormant during the winter, and germinating (under favour- 

 able circumstances) during the following season. 



We have now glanced at the fungus and its effect upon the 

 foliage and stem ; but we are all of necessity most interested 

 in its fatal effects upon the Potato itself. In the vast majority 

 of instances the fungus makes its first wholesale attack upon 

 the leaves, sending its destructive mycelial threads down the 

 leafstalks into the stem, and thence, and lastly, into the 

 Potato itself. If this takes place when the Potato plants are 



«c.s 

 Fig. 7. — Peronospora alsinearum, enlarged four hundred d i a m eters. 



young, growth is at once arrested ; but if the plants are well 

 established, the tubers are found to be discoloured. This is 

 undoubtedly caused by the presence of the fungus beneath the 

 cuticle of the Potato ; for if the Potatoes are taken up and 

 kept in a damp air for a day or so, the perfect parasite pre- 

 sents itself upon the surface. From the exterior of the Potato 

 the fungus penetrates to the interior, decomposing the tissues, 

 and making the tuber a suitable nidus for various other fungi, 

 which are not long in making then appearance. With the 

 decomposition comes the disgusting odour so well known in 

 connection with diseased Potatoes ; the diseased tuber is now 

 attacked by insects, and its end is one horrible fcetid mass. It 

 generally happens that the eyes are the last to succumb to the 

 disease ; and it is stated, that if these are cut out and planted, 

 they grow into healthy plants ; but if the fact is taken into 

 consideration of the resting spores being produced within the 

 intercellular passages of spent Potatoes, and that these resting 

 spores are capable of lying dormant during a whole season, it 

 seems reasonable to imagine that the planting of such eyes 

 would be the one certain means of spreading the disease. 



That the fungus attacks apparently healthy plants there can 

 be no manner of doubt, the prevailing opinion now being that 

 it is by no means necessary that a plant should be in ill health 

 for a fungus to find thereon a suitable nidus. Contrary 

 opinions have, however, long been held, and are still held on 

 this point, many observers thinking that excessive moisture, 

 over-cultivation (if such a thing be possible) , electric influences 



