CHAP. II. DIFFERENTIATION OF THE THALLUS. SIMPLE SPOROPHORES. 47 



FlG. 20. Phytophthora infestans, extremity of two simple sporophores. a forma- 

 ion of the first gonidia on the tip of each branch. * two ripe gonidia on each branch, 

 vith the beginning of the formation of a third. Magn. about 200 times. 



put out branches bearing new sporangia. There is here therefore a cymose branching 

 of the sporangiophores. 



The gonidiophores in Peronospora, which are also without transverse septation, 

 are repeatedly forked or monopodially paniculate. The branches are all at first 

 narrowly conical, and when their longitudinal growth is completed their terminal 

 portions swell into an ovoid form, as is seen in Fig. 20 a, and are abjointed to form 

 gonidia, and with this the de- 

 velopment of a gonidiophore 

 of Peronospora conies to an 

 end. But in the nearly allied 

 genus Phytophthora after 

 the abjunction of each goni- 

 dium the narrow end of the 

 branch which bore it swells 

 slightly immediately beneath 

 it, and elongating at the same 

 time pushes the gonidium so 

 much to one side that it pre- 

 sently forms a right angle 

 with the pedicel. Then in P. 

 infestans the gonidiophore 

 swells at the point of attach- 

 ment of the gonidium into a 

 small narrowly flask-shaped 



vesicle, and its upper end elongates at the same time and again assumes the character 

 of a gonidia-forming point. After a time a gonidium is formed on it in the manner 

 described above, and the process is repeated usually three or four times on the same 

 gonidiophore, or as many as twelve or fourteen times in luxuriant plants. Older simple 

 gonodiophores therefore, when examined dry, are 

 seen to bear a number of lateral nearly equidistant 

 gonidia forming a right-angle with the gonidiophore, 

 and each standing on a flask-shaped swelling 

 (Fig. 20 b). As the ripe gonidia fall off instantly 

 in water, preparations treated with water have the 

 older branches of the gonidiophore swollen at inter- 

 vals into the shape of a flask with a single unripe 

 gonidium at most at its apex. 



The simple sporophores of Haplotriehum, 

 Qonatobotrys, and Arthrobotrys (Fig. 21) are 

 short erect rows of cylindrical cells usually simple, 

 but sometimes with single branches. The apex of 

 the uppermost cell swells up considerably in Haplo- 

 triehum, slightly in the other species, and puts out 

 numerous crowded protuberances, which together 

 form a small spherical head and develope into 

 gonidia. This is the whole of the development in 

 Haplotriehum. But in the other two forms the 

 apex of the gonidiophore begins to lengthen again 

 after the first head is matured and grows through 

 it, and thus the head becomes a whorl surrounding 

 the flanks of the gonidiophore ; the growing end 

 of the gonidiophore attains to about the length of one of its lower segments, be- 

 comes septate above the first head and then forms a new head at its extremity like 

 the first. This proceeding may be repeated several times, till the gonidiophore is at 



FIG. 21. Arthrobotrys oligosporA, Fres. a sim- 

 ple sporophore springing from the my cclial hypha 

 m with the first head of gonidia. * second head 

 above the first, c old sporophore with the trace 

 of five successive heads. After Fresenius (Beitr). 

 a and c magn. about 200 times, 6 less highly mag- 

 nified. 



