CHAPTER VII—PHENOMENA OF VEGETATION.—PARASITES, 389 
Phacidium &c., must be added to the list,— species which commence their vegetation 
on the living leaf, and complete their development by forming their sporocarps on 
it when fallen and decayed in the next period of vegetation, and here too at the 
expense of the reserve of food obtained from the living host. How far the building- 
material required for the last section of the life of the plant is partly taken from the 
dead decaying leaf has never been thoroughly investigated and can scarcely be 
determined with entire certainty. But this supply of material can be at most only a 
small addition, since on the one hand the Fungus-body, separated from the sur- 
rounding substance of the fallen leaf, also reaches its normal and complete develop- 
ment, and on the other hand it can be seen directly that the reserve material. stored 
up in the Fungus-body is used up in the course of this development. It is possible 
that in this case also intermediate forms and shades of difference may occur, in which 
a final stage of enforced saprophytism succeeds the parasitic vegetation, in the way 
described above on page 373 in the case of Cordyceps. 
Section CXI. The purely local circumstances connected with the spread of 
parasites on plants from the place of attack need no further discussion in the case of 
hosts formed of one or few cells, because the parasite must necessarily remain 
narrowly localised in and on so small a body; and the remark equally applies to 
those which like the Synchytrieae live in single cells of larger plants. 
Parasites which form mycelia in more highly organised and especially in 
phanerogamous plants behave very differently according to the species or to the 
segment of their development; in the one extreme they are confined to the immediate 
neighbourhood of the point of attack, in the other they spread wrdely or unlimitedly from 
that point over or through the host. 
From among the many species which have been noticed from time to time in 
former sections of this book and in addition to them, we may name here as examples 
of the first category the parasites which form narrowly circumscribed spots on the 
leaves of Phanerogams, such as many Uredineae, and among them Puccinia graminis, 
P. Rubigo vera, Uromyces Phaseolorum, Peronospora viticola and P. nivea (Umbelli- 
ferarum), Protomyces macrosporus, Entyloma Calendulae, species of Polystigma and 
Rhytisma. Each distinct spot inhabited by the Fungus is the result of the growth of 
one or occasionally of several spores. Fresh spots are added one after another on a 
surface in: proportion as new spores from any quarter, for instance from those first 
established on the leaf, germinate there and assail it. The species of Claviceps are 
confined to the flowers of Gramineae and Cyperaceae during the whole of the 
parasitic portion of their life, and destroy the young ovary in the manner described 
above. The germ-tube of one spore at least is required to infect each ovary, and it 
attacks the ovary directly. 
Among the Fungi of the second category which spread far from the point of 
attack are the often mentioned Sclerotinieae, Pythieae and Phytophthora, which 
assail the host at any point and grow through it to an unlimited extent in every 
direction, provided the external conditions are favourable. Cystopus candidus is 
instructive as an instance of strictly obligate parasitism. Its germ-tubes find their 
way into every stoma in Lepidium sativum and Capsella on which germinating spores 
fall (page 363). But those germs only develope further which have penetrated into 
the cotyledons, and the mycelium may spread from them through the entire host as 
