366 



BOTANY 



In the life-history of the Uredineae provided with such trimorphous chlamydo- 

 spores still another asexual sporiferous fructification occurs, resulting in the pro- 

 duction of conidia. In this case the conidia are formed in pyonidia similar in form 

 and structure to those exhibited by many of the higher Ascomycetes. The pyc- 

 nidia'produce internally minute conidia on filamentous conidiophores, the so-called 

 pycnospokes or pycnooonidia. The pycnidia were formerly called spermogonia, 

 and the spores, which were thought to be sexual cells, were then termed spermatia. 

 The pycnooonidia are discharged from the mouth of the spherical or flask-shaped 

 receptacle (Fig. 289) ; their further development on the host-plant is still unknown, 

 but they may be induced to germinate in a nutrient solution., The pycnidia 

 appear in spring with the secidia, but somewhat earlier, and on the upper side of 

 the leaf, while the secidia develop on the under side. 



The Uredineae thus exhibit a great variety of asexual spores, as in addition to 

 the three chlamydospore forms they produce two other kinds of conidia, viz. those 

 formed in the pycnidia and on the basidia. The different spores usually succeed 

 each other, according to the seasons ; aecidiospores and pycnooonidia in the spring, 

 uredospores in summer, and teleutospores in autumn, which in the following spring 

 develop basidiospores. The latter germinate at once, and the mycelium penetrates 

 the host -plant and produces in turn secidia, pycnidia, etc. jEcidiospores and 

 uredospores provide for the dissemination of the Fungus during the vegetative period. 

 All the different forms of spores arise in the course of the year, either on the 

 same host-plant, or the pycnidia and secidia may occur on one host-plant, and the 



uredospores ' and teleutospores on an- 

 other, often unrelated plant. In the 

 first case the parent Fungi are termed 

 autcscious (e.g. Puecinia Porri on 

 species of Allium and P. Asparagi, 

 the Rust Fungus of Asparagus) ; in 

 the latter instance they are heter- 

 cecious, and an alternation of hosts 

 occurs. 



An example of an heteroecious Rust 

 Fungus is afforded by Puecinia gram- 

 inis, the rust of wheat. It develops 

 its uredospores and teleutospores on 

 all the green parts of Gframineae, 

 especially of Rye, Wheat, Barley, Oats, 

 Transverse section to which its parasitic mycelium is ex- 



Fig. 289. — Puecinia graminis. 



of a leaf of Barberry with a pyenidium in 

 longitudinal section (xl50); r, escaping pyeno- 

 spores ; 2, a portion of the hymeniura of the 

 pyenidium ( x 225) ; 3, germinating pyenospores 

 with several oil globules shown in the long 

 germ-tabe ( x 360). (After v. Tavel.) 



tremely injurious. The secidia and 

 pycnidia of this species are found on 

 the leaves of the Barberry (Berieris 

 vulgaris). In the spring the hiber- 

 nating double teleutospores give rise to 

 transversely septate basidia, from which 

 the four basidiospores are abstricted (Fig. 288, 2). These are scattered by the 

 wind, and if they fall on the leaves of the Barberry they germinate at once. 

 The germ-tube penetrates the cuticle, and there forms a mycelium which gives 

 rise to pycnidia on the upper side of the leaf (Fig. 289), and to secidia on the under 

 side. This form of the Fungus is known as uScidium Berber idis ; the secidium 

 resembles essentially that of Puecinia fusca previously figured (Fig. 287). On the' 

 rupture of the peridium the reddish-yellow tecidiospores are conveyed by the 



