FUNGI. 265 



large proportion of the Order probably no other mode 

 of reproduction obtains. In several genera however the 

 life-history of which has been more fully worked out, 

 a true sexual reproduction, determined by the contact 

 or confluence of the contents 'of distinct cells, often in 

 but very slight morphological contrast, occurs. The pro- 

 duct of this sexual generation varies in the different 

 groups of Fungi. 



Though a few of the Fungi are esculent, many are 

 dangerous, and some poisonous. None should be eaten 

 unless perfectly sound, and species with a disagreeable 

 odour should be avoided. Many Fungi are very injurious, 

 destroying large quantities of agricultural produce, timber, 

 and miscellaneous substances, when circumstances favour 

 their development. The Wheat Mildew, Smut and Bunt 

 of Corn, Ergot, Hop-blight, the Moulds, and Dry-rot, 

 as well as the microscopic unicellular genera which are 

 the active agents in putrefactive and fermentative change 

 in organic substances, are all Fungi. The Vine and 

 Potato diseases are also due to the ravages of minute 

 entophytal species, which multiply with great rapidity. 

 As their spores are excessively minute, they cannot be 

 excluded by any mechanical contrivance. 



6. Natural Order Algas. The Sea- Weed Family. 



This Family includes an enormous number of chloro- 

 phyll-containing species, nearly all adapted to grow under 

 water, though by no means all marine, as many are 

 wholly confined to fresh water. The characteristic green 

 colour of the chlorophyll is in many genera disguised or 

 concealed by a red, violet, or brownish pigment, the 

 presence of which is so conspicuous as well as constant in 

 certain groups, especially of Marine Algae, as to serve 

 provisionally for their systematic distribution. The Algse 

 vary to an extraordinary extent in size, form, and mode 

 of reproduction. Some are microscopic and individually 

 invisible to the naked eye ; whilst others, especially some 

 marine species, attain a large size a few, indeed, mea- 

 suring some hundreds of feet in length. The simplest 

 forms consist of single microscopic cells ; hence they are 

 often spoken of as Unicellular Algae. These multiply by 



