Seed or fruit

Can there possibly be a dispute?

At Ohaupo Elementary School one of my sons had to learn this verse from one of Dr. Seuss’ children’s books: “I am the Lorax. I speak for the trees. I speak for the trees for the trees have no tongues….”.  But I’d like to add (and it even rhymes) “But trees do have seeds” and with few exceptions like bananas and a few other domesticated species, the trees need them to produce new trees. And this brings me to this week’s BIOFORTHEBIOBUFF topic, for I collected something that some people call seeds and others fruit. The latter are typical of Angiosperms, i.e. the flowering plants. The fact that they appeared rather abruptly about 100 million years ago and are not known from before that time troubled the great Charles  Darwin to an extent that he called the evolution of the Angiosperms “an abominable mystery”.

On the campus of Andong National University in Korea, we have many Ginkgo biloba trees, but they are not Angiosperms, but Gymnosperms. I remember a thing or two about them from my high school bio-classes with Dr Ruppolt, e.g. that the species is dioecious and that therefore separate male and female trees exist, that the species is ancient and has survived in China unchanged for 200 million years and now has been introduced to many countries, because it is such a tough and long-lived tree. Its pollen grains are wind-dispersed and, unique among all of the different species of trees and all flowering plants, contain sperm cells with cilia. Although the ginkgo tree is related to needle trees, it does not have needles but possesses characteristically shaped, parallel-veined, bilobed leaves (hence the specific name “biloba”), which turn beautifully golden in autumn and drop to the ground.

What I was not taught was, that its cherry-sized, yellowish  -let me call it for the moment- “fruit”, has a reputation to smell like vomit or rancid butter. This was the reason why my wife chased me out into the garden with my big bag of ginkgo “fruit”, which I had collected at the university and proudly presented to her when I got home from work. Although the ginkgo seeds, known as ‘nuts’ are edible when freed from their soft and yellowish coat, it takes time to wash, dry and then boil or lightly roast them before they can be consumed. But does the ginkgo tree actually produce “fruits”?

The tree, as mentioned before, belongs to the Gymnosperms, i.e. needle trees like conifers, which are characterised by an absence of flowers and the presence of naked seeds. The berries that a few of the Gymnosperms such as ginkgo, yew and juniper produce, look like real fruits, but they are derived from the ovule’s outer layer around the seed inside the ovary and are not, as in the flowering plants (known as Angiosperms), the result of the plant’s entire ovary. The latter is what in the Angiosperms enlarges and then becomes a proper fruit. Technically speaking, therefore, ginkgo, yew and juniper do not produce fruits, but only coated seeds that lack the ovary’s protective surround. In case of the yew, its red and sweet seed coat is edible and delicious, but its seed is deadly poisonous and should never be swallowed; the juniper berry is used for meat dishes (and gin), and regarding the ginkgo nut, only the adequately prepared seed without its fleshy coat is used.

What I found strange is that I do not find the ginkgo “fruit” smelly at all, while everybody, even those in Japan and Korea who love to eat the nuts, say so. I may have what the sensory physiologist John Amoore called “specific anosmia”, which applies to people who have an otherwise normal sense of smell, but are unable to smell certain specific odours. The Chinese writing for ginkgo 銀杏 (also used in Japan) translates into “Silver Apricot” (and not into something like ‘vomit berry’ or ‘stinky nut’). Perhaps the one who invented this Chinese character also was a lucky person who had specific anosmia and was not bothered by the ginkgo nut’s smell.

© Dr V.B. Meyer-Rochow and, 2021.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content. 

biology zoology blog benno meyer tree bark

Trees have a bark

You can see it but can’t hear it

I love going for a walk in the forest and the other day I was saying to my Korean friend that perhaps I should write a blog about the trees’ bark. She cast a surprised look at me and uttered “I’ve never heard a tree bark!”. Well, she had studied French for 5 years and her English is still not perfect, which is why she must have thought of “aboyer”, the barking of a dog. Anyway, although the bark of a tree cannot be heard, it is an interesting and in some ways puzzling part of the anatomy of all woody plants. Consulting the botanical literature, you will learn that botanists distinguish an inner bark, which transports assimilation products from the leaves or needles downward, and an outer bark, whose outermost structure is what we see when we look at the stem. You will come across some scientific terminology like ‘the vascular cambium’ as the tissue located between the inner and the outer bark responsible for giving rise to the bark. You will read about the ‘phloem’ as the tissue that is responsible for the transport of the sugars that result from the photosynthesis in the green leaves or needles and you will learn that what the non-botanist calls the bark is to a botanist the  ‘rhytidome’, a  waterproof structure of cork and dead cells that consist of cellulose and lignin and is confined to the outer bark.

With regard to the function of this outer bark, its protective function is always highlighted: protection against mechanical forces and fire, against potential pathogens and herbivores, against vines and other “climbers” and to prevent colonization by epiphytes, lichens and algae. However, why there should be this enormous variety of bark types and structures is largely left unexplained, especially in view of the fact that trees had more than 300 million years to ‘perfect’ the appearance of their bark to meet all the functions mentioned above.

Walking in the forest and seeing tree species with smooth or exceedingly rough, flaky or almost scaly barks and encountering in which the outer bark is covered in sharp protrusions and spines or resembles loose and smooth sheets that come off easily or consists of strips that either peel off horizontally or vertically, you cannot but wonder whether the explanations for the tree barks’ functions aren’t perhaps incomplete. Sure, barks with spines make it hard for tree-climbing mammals to ascend them, but not for insects. On the other hand, trees with rough and scally barks like many pine trees make it easy for arboreal mammals, e.g. squirrels, to climb them, but cause small and crawling insects a terrible problem.  Smooth barks and trees in which the bark can come off in large sheets leaving an almost polished stem behind like in many eucalypt trees, must be a nightmare especially for mammalian climbers.

I therefore believe that the bark of at least some tree species is designed not to prevent, but to facilitate the ascend of fruit-eating animal species, as the seeds are usually indigestible and the fruit-eater helps to spread the tree species by releasing the seeds with its faeces. Not all insects are disliked by trees and ants are in fact welcome as they prey upon a tree’s unwanted pest insects, deposited on them as eggs by flying species, primarily moths and butterflies. Moss and lichens growing on the bark and not harming the tree at all could assist beneficial insects like ants in ascending the tree. The idea that the bark of certain trees has evolved features to assist animals to climb them has not received much attention, but I think it should be worth a closer look.   

© Dr V.B. Meyer-Rochow and, 2020.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.