For March, 1920 



109 



In botanical language, the outer coverings of seeds, which may 

 be one or more, are given names, as pericarp, &c., according lo 

 their exact part in the seed's make-up, and the word seed-case 

 can be taken as including all the various terms used in botany to 

 designate the outer coverings of seeds. Seeds differ consider- 

 ably in the hardness of their coverings, not only as regards dif- 

 ferent species, but also in respect of seeds of one kind, and some 

 take a very long period before the softening process is com- 

 plete : further, the nature of the seed-cases of some seeds is such 

 that they do not readily absorb and transmit water at growing 

 temperatures. Some seeds of this character may lie in the ground 

 for weeks, months, or even years without swelling, anl plant 

 raisers have adopted various methods to artificially e.xpedile the 

 process, such as stratification in moist sand kepi just above freez- 

 ing point in which the seeds are allowed to reinain through the 

 winter months and then sown in the spring ; also hot water is used 

 for the purpose. 



Sometimes when the outer case is a very hard shell, like that 

 with nuts, the shells have first to be cracked, or the same thing is 

 brought about in nature by the action of frost. While all ordi- 

 nary garden seeds will, under the usual soil conditions as regards 

 moisture, absorb sufficient water, some require a very much 

 longer period to accomplish this than others, and with these lat- 

 ter, such as parsley and corn-salad, and with others as well, ger- 

 mination can be hastened by soaking the seeds before sowing in 

 warm wate"- -l-e t' nii)crr'ti-re of '"hich shonM not exceed 100 F. 

 Care should be taken not to soak the seeds too long and they 

 should be taken out of the water as soon as they are swollen and 

 sown immediately. This process should not be started unless 

 the soil conditions and temperatures are right, otherwise the 

 soaking will do more harm than good. 



Necess.\ry Temper.kture for Seed Germin.vtion 



.\fter seeds have absorbed sufficient moisture, the next step 

 in germination is a high enough temperature, and the seeds of 

 some species of plants, and even varieties of the same species 

 will germinate at a lower temperature than will others. It is in- 

 teresting to note that the absorption of water in no wav by 

 itself starts the necessary chemical changes in the seed. These 

 changes do not begin until the embryo commences its activity. 

 Unless the temperature is high enough for this activity to start 

 within a comparatively short period (so far as ordinary garden 

 seeds are concerned) after the seed has become sufficiently moist, 

 the seed generally rots. Therefore the various procsses neces- 

 sary to prepare the food of the plantlet do not begin until after 

 the germ of the seed has started into active life. 



It goes almost without saying that it is rare to find a sanink- i)t 

 seed containing 100 per cent with living embryos, and it is scarcely 

 necessary to remark that no treatmcm can put life into a dead 

 seed. Then, too, the embryos vary in their strength, or in the 

 amount of vitality they possess. Some will sprout and then die. 

 while others may not have sufficient strength to push their wav 

 out of the ground. These things happen when the surrounding 

 conditions are perfect ; when some or all of the conditions are less 

 perfect, then a larger proportion of the viable seeds will fail to 

 complete the act of germination. 



As seeds of their kind vary in size, there is a greater amount of 

 total plant food in heavy than in light-weight seeds, and the ad- 

 ditional reserve of food in heavy-weight seeds enables the plantlet 

 to reach a more advanced stage of growth before being compelled 

 to collect and assimilate food from the soil. The additional 

 strength of plantlets from heavy seeds prevails more or less, in the 

 case of annuals, throughout their life, and thev will invariablv 

 come to maturity sooner. The advantages of using seeds which 

 arc the heaviest of their kind is obvious, and commercial lettuce 

 growers, for instance, have found that by screening the seeds 

 and usmg only the heaviest, thev arc able to produce one more 

 crop durmg the winter half of the year than thev can when 

 unscreened seeds are used. 



Sometimes the plantlet exhausts the food contained in the seed 

 before reachmg the surface, and of course this is more likely to 

 happen m the case of light .seeds than with heavy ones, although 

 It the seed is planted too deeply or the soil conditions are bad 'it 

 may occur with the heaviest seeds. If the food in the seed is ex- 

 hausted before the act of germination is complete, that is before 

 the sliool of the plantlet has come up above the ground growth 

 ceases as plants cannot assimilate food until the green sub- 

 stance ,n the leaves, known as cholorphyll has been formed ' be- 

 cause all the organic compounds of plants are produce.l in the 

 leat-relLs which cannot take place except in daylight, although iho 

 electric light does ,n some degree take its place. It mav be 

 ul. "\ <^°"""«''^l;"<:tion to this, that the shoots from bulbs 

 ubers and other fleshy roots will keep on growing in the dark, 

 no,!*' ■ : 'lowcvcr takes place by means of the reserve <,f plant 

 chemicT","" '" ""' bulbs, etc., in which somewhat similar 

 chtmical action goes on as is the case in the seed 



semi\'rtn"!l,"";: '^''^"""'' P'lysiological, or biological changes es- 

 sential to the development ot plant fond in the soil can take place 



in the absence of the stored up enegry in the soil indicated by tem- 

 perature, a statement which applies with equal force to seeds. 



There is for most seeds, a certain range of soil temperature 

 under which germination is most rapid : under which the plantlets 

 are the most vigorous, and which ensures the highest percentage 

 of plants from a given quantity of seed. Seeds of different species 

 and sometimes varieties of the same species, have (1) a minimum 

 temperaiure at which they will germinate at all, (2) an optimum 

 temperature at which germination is quickest, and (3) a ma.\i- 

 mum temperature beyond which germination does not lake place. 



Most people know that freezing point (32 F.) is really the de- 

 gree at which ice thaws and it is no uncommon sight to find 

 grain in the straw of an ice-house germinating between cakes 

 of ice. 



We have pointed out the first necessity as being to have the 

 soil in a suitable condition before sowing seeds ; which condition 

 will not arrive before the lapse of some days after thawing — 

 sooner in a sandy soil than in a clayey one — during which period 

 the temperature of the soil at the depth of sowing will invariably 

 reach at least 35 degrees. Peas are among those plants having 

 varieties differing in hardiness, and while we can sow round 

 s; eded kinds. Alaska for instance, any time in March the ground 

 will work properly, it is not safe to sow those varieties having 

 wrinkled seeds so early. Of course we may have bad weather 

 after sowing, but during many years of experience I have never 

 had a failure with Alaska peas although sometimes wet and 

 freezing weather has subsequently followed ; the earliest date of 

 sowing has been March Slh. It is sometimes true that peas sown 

 in .\pril will come into use as early as those sown in March, but 

 all other things being equal, the March sown ones invariably 

 give more produce because, although the tops of the March 

 sown ones may have made slow .growth, they have used the 

 period in making more growth at their roots and are therefore 

 better able to withstand hot weather in May and early June than 

 those sown in April. 



Most people know tliat the flavor of the wrinkled-seeded varie- 

 ties is superior to the round ones, but under the same condi- 

 tions and sown at the same time, the latter are always a week 

 or more earlier. Upon sandy soi's especially, it is worth while 

 towards the end of March to risk some of tlie wrinkled kinds as 

 the_y sometimes go through all right. In the case of Sweet Peas, 

 white seeds will not germinate under such adverse conditions as 

 those of a dark color. 



In the case of the wrinkled varieties of edible peas and the 

 white-seeded sweet peas, it appears that it is not the degree of 

 actual cold which affects them, but wdien harm is caused it is in- 

 variably due to a more or less prolonged perir d of co'd rain after 

 sowing and before germination, and this is especially noticed upon 

 badly drained and shallow worked soils. After germination has 

 started, very early sown things will withstand adverse conditions 

 of greater magnitude than they can before. When germination 

 starts there is always a slight rise in temperature within the 

 seed, due to heat being produced by the oxidation of some of the 

 starch ; in fact this rise in temperature is brought about by exactly 

 ihe same process as that which produces heat in the bodic"s of ani- 

 mals. 



While we need not trouble about temperature in the early sow- 

 ing of such things as peas and spinach, so long as soil conditions 

 are favorable, y^et, as the season advances and we begin to handle 

 less hardy species, soil temperatures require to have greater con- 

 suleralion, as more vigorous plants are produced when the soil is 

 warmer. Probably the most troublesome vegetable in northern 

 districts IS the pole lima bean, and it is becoming a common prac- 

 tice to sow this bean in shallow boxes in a cold frame and plant 

 them out later on; this is the surest way of handling this vege- 

 table especially on a clay soil and in localities with a short sum- 

 mer. It would be only waste of time lo sow lima beans when the 

 soil temperature is as low as 49 degrees, but a start mav be made 

 with .string; beans at that temperature, especially with' the black 

 seeded varieties, and bush limas will germinate at a lower tem- 

 perature than the pole variety. Now and then the less hardv vege- 

 tables which have germinated at ihe end of April or earlv^n 

 May are damaged or killed by a Mav frost, and this happens 

 more frequently in low-lying districts and upon a wet soil • at the 

 same time it is always worth while to take a little risk on the 

 chance of getting some beans and corn from one's own garden a 

 little earlier than is usual in the locality. 



Oxygen Essk.vti.m. for Seed Ger.min,\tion 

 As is the case with all living organisms, the embrvo contained 

 in the seed requires oxygen for its development, and without it 

 even if all other conditions arc suitable, germination will not 

 commence A supply of oxygen in the soil is only assured when 

 the gr Hind has been ili,.roughly worked an.l is friable and mel- 



Careful observations along the lines of experimentation have 



proved, in many ways, thai when oxygen is completelv excluded 



rom s<-eds, that are otherwise placed properly for germination, 



they fail to start. Ii has been found, too, that even after a 



