Lehman: Conidial Formation in Sphaeronema 161 



subsequently liberated by a tangential splitting of its walls to 

 form an outer sheath, the thickness of the sheath, as well as of 

 the wall of the conidium, should be half that of the wall of the 

 conidiophore before conidial formation. Instead of this, one 

 finds that the wall of the conidium is nearly, if not quite, as 

 thick as that of the sheath surrounding it. The sheath does not 

 appear thinner than the apical wall of the conidiophore before 

 cdhidia formed within it, nor less thick than that of the basal 

 portion of this cell (Figs. 8-n). 



2. It is clearly seen from Figs. 8-1 1 that the end of the proto- 

 plast of the conidiophore is not naked but protected by a wall 

 fully as thick as that about the conidium above it. It is believed 

 that this wall extends for some distance back from: the tip. In 

 Fig. 6, at (b), the wall of the protoplast is clearly separated 

 from the sheath. At (c) the wall presses so closely to the sheath 

 that the line of separation cannot be distinguished although they 

 appear separate again at (a) for a short distance. In Fig. 7, the 

 protoplast is seen to have grown beyond the sheath for a con- 

 siderable distance without having formed conidia. It is invested 

 with a delicate wall which is separated from the sheath for almost 

 one-half the length of the conidiophore. The fact that this proto- 

 plast clothes itself with a wall for a distance from its tip greater 

 than the length of a conidium indicates that the conidia are not 

 formed by direct septation of the conidiophore and that the 

 sheath takes no part in the formation of the conidial wall. The 

 septum cutting off each conidium must arise from the new wall 

 with which the protoplast invests itself and not directly from the 

 wall of the conidiophore. 



3. In several instances conidia, as illustrated in Fig. 12, have 

 been observed which had germinated prior to escape from the 

 conidiophore. This indicates that conidia mature while still 

 wholly within the sheath. 



On the basis of the evidence presented and discussed above, 

 in which conidial formation for Sphaeronema seems to differ 

 from Thielavia, the first and often the second, hyaline conidium 

 in a series can properly be regarded as an endoconidium. It is 

 clearly delimited within a closed cell whose wall remains intact 



