May be due to silica and pufa content in the stem

Please go through the attached article.

Dear Arvind Singh Ji,

An exhaustive and useful data.

Thanks

Regards

Vijay

A plant's ability to resist breakage depends on the location and prevalence of tissues containing parenchyma, collenvhyma 

A plant's ability to resist breakage depends on the location and prevalence of  tissues containing parenchyma, collenchyma and schlerenchymatous cells.  The more the schlerenchymatous cells the more the mechanical strength and so the plant is more able to resist pressure and breakage. 

Dear Colleagues

Thanks for all participants

The reason is physical not anatomical  

Plants have different types of cell and tissues Tissues are group of cells having similar function Like Xylem and Phloem are tissues whichhave different type of cells mainly for conduction. 

Similarly there are tissue which support the plant structure. In young growing dicot plants such tissues are from Pectin  which is easily stretchable like collenchyma which has thickening of pectin on end walls. Older tissues have much thickened walls and this wall comes from Sclerenchymatous tissues ( fibers and stone cells) These tissue contain Lingnin in their walls which can not be bend It will break  The relative amount of these two types of tissues determines if the plant will bend or stand in strong winds. Monocots have sclerenchymatous tissue in young stages also and hence the lodging takes place in strong wind and plants can not standup again. 

Thus its relative amount of tissue type and secondary growth which determines if the plants will bend or break in strong wind 

Dear Dr. Ashwani Kumar Esq

You refer the cause to anatomical aspects, the real cause is physical combined to cell wall ultra structures,    

At a gross level, mechanical strength is a function of dry matter/length of the stem.  This indirectly also accounts for the diameter.  Within the dry matter, proportion of cellulose is main determinant of strength.  Although not separately published, it is described in brief in the attached documents.

Fig. 8 in the attached patent contains valuable information on contribution of different maize stalk parts to mechanical strength.

strength of the stem depends on the rigidity of cholenchyma,  sclerenchyma and total cellulose content.

Colenchyma is usually occurred in short lived stems and leaves grasses and deciduous leaves.

Flexibility is due to the parallel and angle arrangements of cellulose  micro fibrils within primary and secondary cell wall layers, arrangements which allow stretching make the stem obey the wind forces that stem exposed to. Thanks for all 

Hi Caser,

The answers to your question can be very broad. It depends on what species and what kind of plants are used for comparison.

1. woody plants stronger than those ex. rice, wheat,....

2. Large woody plants, in general, stronger than smaller woody plants...

3. If same species and same variety, a healthy plant stem can be stronger than unhealthy plants (such as disease-infected, stressed...)

4. The shape of the branches with leaves can be a factor too, see attached photo. In the photo, the branches and leaves have been artificially shaped in such a way that reduce the 'impact' of wind, compared to other shapes of the same plants

5. When you said "Flexibility is due to the parallel and angle arrangements of cellulose micro fibrils.....", what groups of plants are used for comparison?

In all plants, we talk about cell walls flexibility depend on how the cellulose micro fibrils arrangements in cell wall layer   

The secondary thickenings on the cell walls  give the required mechanical strength to with stand the pressure

Assuming we're dealing with lateral winds only, a flexible plants stem would act as a cantilever beam under uniform load. Assuming we're not allowing relative movements between adjacent cells, the cell will be subject to bending stress, with its windward wall undergoing tension and its leeward wall compression. The amount of stress suffered will vary according to the cell's length, wall thickness and position in the stem. 

I do not know of a great many studies studying the mechanical properties of cells at this level, this is one of the few I know of:

Simply put it is as a result of their growth habit. This feature defines the anatomical make up of the plant, which in turn explains physical properties. Resistance to wind depends on the topology and edaphic features of the environment in combination with the plant habit and direction of growth.

Palm trees are known to be very resistant to winds and fire. Its unique architecture and unique vascular system ensure a rigid and very efficient structure. Thats a good research please see below:

REGENERATION STRATEGIES OF PALMS (ARECACEAE) IN RESPONSE TO CYCLONIC DISTURBANCES

https://researchonline.jcu.edu.au/48170/1/48170%20Latifah%20et%20al%202016.pdf