6 .GENERAL MORPHOLOGY. 



formod under normal circumstances ; consequently there is, in 

 this case, no separation of the elongating tubular bud into inner 

 and crown cells. In such event the resulting mycelium consists, 

 as already stated, of a single, many-branched, tubular, non- 

 septated cell, such as is shown in Fig. 91. 



The foregoing statement that the inner cells do not play any 

 further part in the mycelial growth of the Mijcomycetes, inas- 

 much as they neither extend in length nor develop septa, may be 

 taken as the rule. There are, however, exceptions, septation, 

 accompanied by elongation, frequently occurring within the 

 inner cells in the event of abnormal conditions of nutrition. 

 This phenomenon is termed intercalary growth, or intercalary 

 septation, to distinguish it from acrogenous growth. 



If, in the absence of external causes of hindrance, the growth 

 of the mycelium is able to proceed equally in all directions, a 

 stellar system of radial, branched threads, with the spore as a 

 centre, is the result. This form of growth was termed a typical 

 mycelium by Zopf. The practical worker in a mycological labo- 

 ratory can obtain such typical mycelia in a youthful condition, 

 and consequently easy to survey, if he re-examines, after a lapse 

 of one or two days, the plate cultures (§85) that have already 

 been examined for the purposes of mycological analysis (e.g. of 

 water, milk, beer). During the fii'st investigation the spores of 

 all kinds of mould fungi from the air will have settled on the 

 solid nutrient medium, each of them then germinating to form 

 a mycelium, and thus yielding, as it were, a self -prepared 

 culture. 



Mention must here be made of one of the various instances 

 of irregular mjcelial development, since it will have to be re- 

 ferred to on a subsequent occasion : this is the phenomenon of 

 intergrowth. It is caused by one of the cells in a mycelium 

 putting forth a branch into the interior of an adjoining cell, so 

 as to displace the intervening septum. The invader may then 

 become divided into cells within the plasma of the invested cell, 

 with the result that an inexpert observer may easily be led to 

 believe that endogenous spores are present. An example of 

 this growth is represented in Fig. 94. Another will be found 

 in a later section dealing with Dematium pullulans, and a third 

 in the case of Oidium Ludwigii Hansen, occui-ring in mucilaginous 

 discharges from trees (§ 248), and investigated by W. Holtz (I.). 

 This was probably also the method of formation of the alleged 

 spores observed by Edm. Kayser (V.) within the hyphae of an 

 unknown mycelial fungus isolated by him from fermenting pine- 

 apple juice. Intergrowths also occur in the sporangia of several 

 fungi. 



In the case of a large number of fungi, the development of 

 the mycelium ceases with the formation of the branched hyphse, 

 the ensuing process being the elaboi'ation of organs of fructifica- 



