COMPARATIVE EFFECTS OF EXPOSURE ON TREES. 
107 
spreading- heads, as in the instance of New Zealand spinach ; and on the other hand 
of plantings closely when plants are required to be tall, and at the same time slender, 
a case which more rarely occurs than the other. 
" Recent writers on botany have endeavoured to show 
that the tapering tube of the carrot, the beet, and other 
simpler plants, are not properly roots, or, at least, that 
they have more the characteristics of stems than of roots ; 
in other words, as every plant g-rows in two directions, 
one downwards, the other upwards, the spindle-formed 
tube of the carrot is alleg-ed to belong to the upper or 
ascending portion of the plant, rather than to the down- 
ward or descending portion. Independent of structure, 
however, this would appear to be equally rational as to 
allege that a man's feet belong to the upper portion of 
his body ; but it appears to be correct enough to say the 
partly horizontal portion of the iris, though underground, 
are not roots but stems ; and it must be very obvious 
that the creeping runners of strawberries are not stems. 
" Weak stems, which cannot rise high in a perpendicular direction by their 
rigidity, are furnished with 
several means for effecting this. 
Some straggle up irregularly 
amongst other thick-growing 
plants, as the bramble and little- 
sweet ; others, like the hop, the 
kidney-bean, and convolvulus, 
twine closely around others 
stronger than themselves, and^ 
when they cannot meet with 
such, several shoots will twine 
around each other to give 
mutual support. 
" It is important to remark, that different species, in twining for support, follow 
different laws, one going from right to left, of which there are twenty genera; and 
another from left to right, of which there are ten genera. A hop-plant, for instance, 
directs its course round a pole with the sun ; but if untwisted and forced to take 
- opposite direction, it will injure or perhaps kill it. If a honeysuckle do not meet 
h support, it twists into a spiral form from right to left. It is of importance to 
own 
an 
with 
attend to these circumstances in training." 
t 
