FREE BOOKS

Author's List




PREV.   NEXT  
|<   130   131   132   133   134   135   136   137   138   139   140   141   142   143   144   145   146   147   148   149   150   151   152   153   154  
155   156   157   158   159   160   161   162   163   164   165   166   167   168   169   170   171   172   173   174   175   176   177   178   179   >>   >|  
erry. Others are woody stemmed plants, persisting from year to year, and often becoming great trees that live for hundreds of years. Still others are climbing plants, either twining their stems about the support, like the morning-glory, hop, honeysuckle, and many others, or having special organs (tendrils) by which they fasten themselves to the support. These tendrils originate in different ways. Sometimes, as in the grape and Virginia creeper, they are reduced branches, either coiling about the support, or producing little suckers at their tips by which they cling to walls or the trunks of trees. Other tendrils, as in the poison ivy and the true ivy, are short roots that fasten themselves firmly in the crevices of bark or stones. Still other tendrils, as those of the sweet-pea and clematis, are parts of the leaf. The stems may be modified into thorns for protection, as we see in many trees and shrubs, and parts of leaves may be similarly changed, as in the thistle. The underground stems often become much changed, forming bulbs, tubers, root stocks, etc. much as in the monocotyledons. These structures are especially found in plants which die down to the ground each year, and contain supplies of nourishment for the rapid growth of the annual shoots. [Illustration: FIG. 93.--_A_, base of a plant of shepherd's-purse (_Capsella bursa-pastoris_), x 1/2. _r_, the main root. _B_, upper part of the inflorescence, x 1. _C_, two leaves: i, from the upper part; ii, from the base of the plant, x 1. _D_, a flower, x 3. _E_, the same, with sepals and petals removed, x 3. _F_, petal. _G_, sepal. _H_, stamen, x 10. _f_, filament. _an._ anther. _I_, a fruit with one of the valves removed to show the seeds, x 4. _J_, longitudinal section of a seed, x 8. _K_, the embryo removed from the seed, x 8. _l_, the first leaves (cotyledons). _st._ the stem ending in the root. _L_, cross-section of the stem, x 20. _fb._ fibro-vascular bundle. _M_, a similar section of the main root, x 15. _N_, diagram of the flower.] The structure of the tissues, and the peculiarities of the flower and fruit, will be better understood by a somewhat careful examination of a typical dicotyledon, and a comparison with this of examples of the principal orders and families. One of the commonest of weeds, and at the same time one of the most convenient plants for studying the characteristics of the dicotyledons, is the common shepherd's-purse (_Capsella bursa-p
PREV.   NEXT  
|<   130   131   132   133   134   135   136   137   138   139   140   141   142   143   144   145   146   147   148   149   150   151   152   153   154  
155   156   157   158   159   160   161   162   163   164   165   166   167   168   169   170   171   172   173   174   175   176   177   178   179   >>   >|  



Top keywords:
tendrils
 

plants

 

support

 

flower

 

removed

 
section
 
leaves
 

Capsella

 
changed
 

fasten


shepherd

 

anther

 
valves
 

inflorescence

 
sepals
 

petals

 
stamen
 
filament
 

examples

 

principal


orders

 

families

 

comparison

 

dicotyledon

 

careful

 

examination

 

typical

 

commonest

 

dicotyledons

 

common


characteristics

 
studying
 

convenient

 

understood

 

ending

 
cotyledons
 

longitudinal

 
embryo
 

vascular

 
structure

tissues
 

peculiarities

 
diagram
 
bundle
 

similar

 

coiling

 
producing
 

suckers

 
branches
 

reduced