(54) 



Aside from what may be called the practical value of the study, in- 

 cluding that which leads to the better understanding of the higher forms of 

 living things, these microscopic creations have many attractions for the stu- 

 dent. Nature is always, and to every one, interesting ;. her pursuit is alluring 

 in the highest degree. To see rare forms men traverse oceans and make pil- 

 grimages over continents ; but here are countless unseen living things, 

 under our feet, on every side, in the air we breathe, in the food we eat, on 

 plants, on animals, germinating and propagating under our own finger nails 

 and even in our mouths, possessing a variety of form and structure, often 

 curious and beautiful, never equalled by art and not surpassed in nature. 

 Their wonderful life-histories stimulate inquiry, engage and enchain the 

 attention. He who possesses a microscope, with the ability and opportunity 

 to use it, need never wander from his own door to find an abundance of 

 material awaiting his researches, and entertaining and instructive biogra- 

 phies ready for his pursuit. (10.) 



The Peronospori^. (11). Among the pests to the cultivators of fields 

 and gardens, the members of this family maintain a bad pre-eminence. 

 None have attracted more attention from the injuries they do to important 

 plants, and from their peculiar and interesting life-history. Formerly 

 classed in widely different groups on account of their difference in structure, 

 the species have been united from their agreement in development. All 

 produce conidia, — naked spores borne upon the tips of erect filaments or 

 /iT/phse, — which in some cases germinate directly and sometimes give origin 

 to some half-dozen zoospores. The latter are small, more or less globular 

 bodies, capable of rapid movements in water by means of two long cilia, 

 which they lash from side to side with astonishing rapidity. They thus 

 swim in a drop of rain or dew some minutes or hours ; then, losing the pro- 

 pelling hairs, settle down, and under favorable circumstances germinate like 

 the conidia by protruding one or more slender tubes, which penetrate the 

 tissues of the supporting plant and become the myceliutn or vegetative 

 threads of the fungus. Besides, through the conidia and their offspring, 

 the zoospores, these particular plants have another method of reproduction. 

 The term oospore has been given to a fruit-body found to arise from the 

 conjoined action of two separate cells of the mycelium. This is a sexual 

 process well known among the algse or sea-weeds, but not yet well made out 

 in most fungi, and analogous to the production of seed in flowering plants 

 by the united action of stamen and pistil. The cell producing the oospore 

 is called a gonosphere or oogonium^ and its partner an antheridium. The 

 oospores are found on or in the tissues of the host, sometimes only upon 

 one of several plants that the conidia are found upon. Unlike the latter, 

 they lie dormant for some months, but, like them, finally give origin to 



10. Cooke's little book on Rust, Smut, Mildew and Mould is an excellent one 

 for a beginner. 



11. The plants enumerated in this paper are from collections made by the 

 author between September 21st and and October 16th, 1876, mostly from the area 

 of ground upon which he makes his home. Any collector will perceive that more 

 of the Uredines and other families are omitted than are mentioned. 



