124 



THE GARDENER'S ASSISTANT. 



soil in which it is growing before it can produce 

 flowers and fruit; in like manner the mycelium 

 of a parasitic fungus does not at once kill the 

 plant in which it is growing, but first accumu- 

 lates a store of reserve food which enables it to 

 form fruit, when the plant attacked begins to 

 droop. At this stage the fungus bursts through 

 the skin of the diseased plant and forms its 

 fruit on the surface. This is the last stage in 

 the life-cycle of the fungus; it has done its 

 worst, having killed the plant, or at all events 

 certain portions of it, when it produces spores, 

 which if placed under favourable conditions 

 enter another healthy plant and follow the 

 course described above. 



Cuttings or portions required for propagation 

 should never be taken from a plant showing 

 disease in any part, as mycelium may be pre- 

 sent in those parts that appear to be healthy, 

 and if mycelium is present in cuttings it con- 

 tinues to grow, and the plant is consequently 

 diseased from the first, although it may be 

 some time before any indication of disease is 

 observed. 



The terrible sugar-cane disease which at one 

 time threatened to put a stop to the sugar in- 

 dustry in the West Indies was proved to be due 

 mainly to the practice of using for propagation 

 what were considered as healthy portions of 

 canes attacked by a fungus. 



For a similar reason the seeds of plants show- 

 ing a fungous disease in any part should not be 

 sown; neglect of this precaution has in many 

 well-proved instances resulted in disaster; as a 

 case in point maybe instanced the "sleeping 

 disease " of Tomatoes, which has been widely 

 spread through using seeds obtained from 

 diseased plants. 



Different Modes of Reproduction in 

 Fungi. — Mo&t parasitic fungi possess two, many 

 three or four different modes of reproducing 

 themselves, each one of which answers a defi- 

 nite purpose in the life-cycle of the fungus, 

 and cannot be performed by any of the other 

 methods. 



As illustrating the mode of life of a fungus 

 having two different forms of fruit, we may 

 take the too- well-known Rose Mildew (Sphcero- 

 tkeca jmnnosa). During the spring the leaves 

 of Rose-trees are often more or less covered with 

 a delicate white mould, which at a later period 

 often passes on to the young shoots and flower- 

 buds. Yen- soon the white mould looks 

 powdery, as if it had been sprinkled with flour. 

 If at this stage of development a minute portion 

 of the mould is placed under a microscope and 



I magnified about 300 times, it will be seen to 

 ' consist of numerous slender branches of my- 

 celium, bearing numerous erect chains of spores. 

 When quite ripe these spores become free, and 

 ; accumulate on the surface of the leaf, giving 

 j rise to the powdery appearance mentioned 

 | above. This is the summer form of the fungus. 



Fi?. lfio.— Rose Mildew (Sphcerotheca pannvm) 



1. Summer form of fruit on Rose leaf (natural size). 2. Chains of spores 

 (magnified 250). 3. Single spore germinating (magnified 250). (Journal 

 Royal Horticultural Society.) 



► . 



The moment the spores are ripe they are capable 

 of germination; and being easily blown about 

 by wind, or carried by insects or birds, those 

 that happen to alight on the damp surface of 

 a healthy Rose leaf or young shoot germinate 

 at once, and within a few days give origin to 

 the mould -bearing spores, which are in turn 

 dispersed. This quick method of spore produc- 

 tion continues throughout the summer months, 

 and as successive crops of spores are produced 

 in immense numbers in rapid succession, it 

 can be readily seen how easy it is for a 

 disease to spread when it has once appeared. 

 As a rule an epidemic is always clue to the 

 spread of the summer form of fruit; in fact its 

 one use is to enable the fungus to extend its 

 geographical range, and where a considerable 

 number of plants of the same kind are grown 

 in close proximity, this function is generally 

 exercised to the utmost, unless special precau- 

 tions are taken to prevent it. 



During early summer the diseased leaves curl 

 and fall, producing only the summer fruit of 

 the fungus, but the diseased patches on the 

 young shoots and fruit continue to grew, form- 

 ing quite conspicuous white velvety tufts, which 

 later in the season produce a second form of 

 fruit called winter fruit. This second form of 

 fruit is much more complicated in structure 



