152 BOARD OF AGRICULTURE. 



the development takes place under circumstances that resistance 

 is less in one direction, they may shoot out in this one direc- 

 tion, and become elongated. This is well shown by columnar 

 or cylindrical epithelium, or by transitional epithelium, as named 

 by Henle, when the cells acquire points, jags and projections 

 in the direction of least resistance, and in the epithelium of 

 the skin. Making a section of the skin, we invariably find 

 flat and closely-packed cells in the epidermis, with the cells 

 on the innermost layer less flattened, and with nuclei. The 

 further we advance inward the smaller do the cells become, 

 the last of them standing in the form of little cylinders on the 

 surface of the papilla? ; the epidermic cells being an advanced 

 stage of growth, in process towards desquamation, the inner 

 layers the formative cells, as shown by the nuclei. Patho- 

 logically, this law is illustrated by cancer-cells, which, like 

 the corpuscles of pus, take their rise from the preexisting cells 

 and nuclei of the texture or organ in which the new growth 

 originates. 



The influence of environment is conclusively illustrated by 

 the study of the development of some fungi, whose spores 

 are vegetable cells analogous to the animal cell. 



When the spores of pencillium crustaceum are scattered on 

 a substance having the same chemical composition as that 

 from which it was taken, a new crop of pencillium crustaceum 

 is the result. 



Now, sow these spores on distilled water, and they swell 

 up and finally burst, with the expulsion of a great number of* 

 minute bodies called zoospores, which finally develop into a 

 plant which has been named leptothrix. 



If these same spores are put under the surface of a liquid 

 rich in nitrogen, the zoospores expelled develop into a micro- 

 coccus ; if the liquid is poor in nitrogen, a cypto-coccus is 

 developed. 



If these spores are sown in milk, which is a fluid rich in 

 nitrogen, we have a micro-coccus appearing, but as the milk 

 sours by lactic acid being formed, the zoospores instead of pass- 

 ing into a micrococcus form, change to an arthro-coccus. 

 If, again, a pencillium-spore germinates on milk just below 

 the surface, we have another form called oidium lactis. 



If, again, a pencillium-spore is sown in fermented wine or 



