Vegetative Organs. 



with an a^ed mternal germ of disease, which he considers in 

 certain cases to be a source of rust, in addition to the ordinary infection 

 by spores. It is often stated that this rust passes the winter as mycelium 

 n such leaves as are attacked in late autumn, and which persists till the 

 following spring; but the examination of hundreds of sections of leaves 

 taken from rusty plants, although not rusty at the place chosen for section. 

 failed to reveal the presence of such a mycelium dormant in the tissues. 

 It may be taken for panted, then, that there is no mycelium to start with, 

 and it will be interesting to follow Eriksson's theory as to the 

 manner in which the mycelium arises afresh in the tissues IB certain cells 

 of the autumn and spring leaves a peculiar thick plasma is found, containing 

 a distinct nucleus, and this Eriksson considers to be, not the ordinary pro- 

 toplasm of the cell, but a mixture of it, with the earliest vegetative form 

 of the fungus. This intimate mixture or symbiosis, or living together ot 

 the ordinary protoplasm of the host and that of the fungus he distinguishes 

 as mycoplasm. This mycoplasm is stated to occur only in certain cells 

 which favours the assumption that it is not a necessary constituent of 

 the cell. 



The next step and the youngest stage of mycelial formation, according 

 to Eriksson, is the presence .of a plasma in the intercellular spaces, which 

 is partly in the form of growing filaments, partly as irregular masses. 

 There are no septa, and no distinctly recognizable nucleus, and even a dis- 

 tinct wall is not formed. The primary stage is quickly followed by a 

 secondary stage, in which the only visible advance is a very distinct nucleus. 

 These two stages are very sharply marked off from the normal mycelium, 

 both by their plasmodia-like nature and the absence of transverse septa, 

 and for distinction the special name of protomycelium is given. Eriksson 

 has no doubt that the intracellular mycoplasm and the inter- 

 cellular protomyctlium are genetically connected, but this, which is a 

 necessary link in the chain of evidence, requires to be further investigated. 

 (Note i, p. 74.) The formation of haustoria is the next) process, and consists 

 in a small straight prolongation of the protomycelium passing into the 

 interior of the cell, and at the apex forming a globular swelling, probably 

 containing a nucleus. Soon the whole forms a sac-like irregular organ, 

 which may become detached from the protomycelium. These detached 

 bodies in the cell were mistaken by Eriksson for a preliminary stage in 

 the formation of hyphae, and called "special corpuscles," but Ward pointed 

 out their true nature, and that they really had been formed by, instead 

 of giving rise to the hyphae, a correction which Eriksson himself has 

 acknowledged. The haustoria are often found closely adjoining the 

 nucleus, which thereby degenerates, and simultaneously with the shrinking 

 of the nucleus, and soon after the first entrance of the haustoria, trans- 

 verse septa begin to be formed in the protomycelium. In most of the cells 

 thus formed several nuclei are contained, and the stage is now reached 

 where a true mycelium is present, composed of hyphae. 



This multiplication of the cells of the fungus is a sign of advancing 

 maturity. By continued division a true pseudo-parenchyma is formed, 

 and at certain spots, where the cells appear to be particularly rich in food- 

 material, a kind of hymenium arises, from which ultimately the spores 

 are detached. Where spores are being formed, there the complete destruc- 

 tion of the cells of the host-plant occurs, and now the vegetative life of the 

 fungus is ended, and the reproductive phase is entered upon. 



