HELIOTROPISM OF ASCI IN DISCOMYCETES 297 



nium ? The answer to this question is provided by a study of the 

 paraphyses. 



As in other Discomycetes, the paraphyses of Aleuria vesiculosa 



^;§| 





1- • rv>( Y/v,-J V^'^ 



V 



Fig. 143. — Diagram of the developmeut of a gymnocarjiic apothecium, e.g. that 

 of Ascobolu.s niagnificus or Pyroneina confluen.<i. Tlie hyphae are repre- 

 sented by short hues the direction of wliich indicates the course of the main 

 hyphae in the different tissues. The ascogenous hypliae are represented by 

 short thick hnes diverging from the ascogonium which is drawn as a circle 

 near the base of the apothecium solely for reference ; actually it is obliter- 

 ated by the growth of the surrounding tissue at an early stage in develop- 

 ment. Asci are drawn in successive stages at the margin of the hymenium 

 in e and/ to indicate the growth of tlie ascogenous hypliae ; but no attempt 

 has been made to show similarly their intercalary growth. The cortical 

 parenchyma is shown by means of thick well -spaced lines without special 

 direction except at the margin, for the palisade arrangement is commonly 

 lost in the mature tissue. Hyphae wliich grow from the underside of the 

 apothecium as excrescent cells into the substratum and which constitute 

 a secondary mycelium are shown by means of a few longer lines. « and b, 

 hyphae growing upwards and enveloping the ascogonium ; these investing 

 hyphae do not form a closed sheath as they do in an angiocarpic apothecium 

 (cf. Fig. 131) ; they continue to grow upwards as a palisade layer which 

 becomes better defined as new elements are added from below, as in stages 

 c and d ; tho- thickness of the apothecium depends primarily upon the 

 extent of this ujigrowth and, as the upgrowth ceases, first in the centre the 

 distal parts of the hyjihae mature into paraphyses. Thus the formation cf 

 the hymenium is started and continues centrifugally until maturity. About 

 the same time the cells in the lower part of the primordiinn begin to enlarge ; 

 the process extends outwards and upwards to the margin, forming a pseudo- 

 parenchymatous cortex. The ascogenous hyphae arise at about stage b and 

 they grow upwards with the sterile hyphae ; the formation of asci begins 

 shortly after the appearance of the paraphyses and is shown in e and/; in 

 / marginal growth is beginning. Drawn by E. J. H. Corner {Trans. Brit. 

 Myc. Soc, Vol. XIV, 1929). 



attain maturity before the asci {cf. Figs. 143 and 144). The para- 

 physes soon grow to their maximum length and then the asci push 

 up between them. Observations on fruit-bodies grown in the 

 laboratory have taught me that the parajihyses are j^ositively helio- 

 tropic. As shown in Fig. 145, which represents a section through 



