1876. ] Hygiene of House Plants. 667 
ceive that what was set forth in the first portion of this article 
will have been abundantly sufficient to disprove the existence of 
this assumed want of moisture in the Mississippi Valley. If the 
drift agencies had covered the whole of the prairie States with 
coarse detritus, as they have the region to the north and northeast ; 
then, in the opinion of the writer, forests would have clothed the 
whole country, as far west, perhaps, as the western border of 
Towa; but from there on, no matter what the condition of the 
surface, they would not have extended themselves, because of the 
deficiency of moisture, the decrease being a very rapid one from 
the 94th meridian towards the west. On the other hand, there 
is nothing in the geological conditions of the surface in the region 
of the plains to prevent a forest growth, provided the climatolog- 
ical conditions were favorable, a complete change taking place in 
the character of the formations soon after we enter Nebraska and 
Kansas, the Cretaceous and Tertiary rocks covering up entirely all 
the older strata; and as they consist almost exclusively of coarse 
arenaceous materials, they furnish by their decomposition a soil 
very different from that of the prairies. If, again, the topogra- 
phy of the country was such that the warm and moist winds 
eould not blow from the Gulf of Mexico up the valley of the 
Mississippi, causing as they go an abundant precipitation, then 
that region would be a sterile one, instead of being, as it now is, 
one of the most favored agricultural areas of the world, albeit 
not everywhere clothed with forests. 
HYGIENE OF HOUSE PLANTS. 
BY GEORGE H. PERKINS, PH. D- i 
ARE plants growing in occupied rooms injurious or beneficial 
to the health of the occupants ? This is a question often 
‘ asked and often answered in a very general manner ; but it does 
‘Rot seem to be always easy to give specific reasons for a belief 
> the value or worthlessness of the influence of cultivated plants 
1 Upon the air immediately about them. As full and satisfactory 
= *Teply to the question we have asked as can be given 18 of con- 
eo siderable importance, now that plants are found growing in a 
= “tge majority of homes all over the country, and to furnish a 
| ply is the object of this article: Although the writer 1s con- 
_ Sous that it is not by any means all that could be desired, he yet 
: hopes that it may not be wholly useless to many lovers an 
_ (Altivators of plants. 
